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The climate crisis: a period of consequences

Climate review written by Dr Aaron Thierry, University of Sheffield, March 2013, updated May 2014

The climate crisis: a period of consequences

Aaron Thierry, PhD

“Owing to past neglect, in the face of the plainest warnings, we have now entered upon a period of danger ... The era of procrastination, of half-measures, of soothing and baffling expedients, of delays, is coming to its close. In its place we are entering a period of consequences.” - Sir Winston Churchill [[i]]

For over twenty years now scientists and world leaders have made increasingly alarming statements about how man’s activities are interfering with the Earth’s climate system and how this would have profound implications for human civilisation if we fail to act. Yet we procrastinate.

Since the Rio earth summit in 1992 CO2 emissions have continued to increase exponentially, with 2012 seeing the second greatest annual increase in the concentration of atmospheric carbon dioxide ever recorded [[ii]]. This has caused levels of CO2 to increase by over 40 parts per million over that time period to its present level of around 400 parts per million (ppm) [[iii]]. Levels of atmospheric CO2 are now higher then they have been for at least three million years.

Figure 1 illustrates the extremely strong correlation between carbon dioxide and temperature of the planet revealed from analyses of air-bubbles, trapped in ice cores from Antarctica. You can clearly see the last four ice ages. When the last of these reached its maximum, about 20,000 years ago, mile high ice sheets covered much of Europe and North America and sea levels were 120m lower than they are today. It is important to realise these huge changes to the planet’s surface where caused by what sounds like a relatively small change of just a 4-5 degree C in the planet’s average temperature.

Figure 1

Figure 1. The correlation between the concentration of carbon dioxide and the temperature over Antarctica the last 400,000 years. [[iv]]

These analyses also reveal just how far outside of historical bounds our fossil fuel emissions have taken carbon dioxide concentrations – the blue spike at the end of the time series. A final important point to note is how historically unusual is the period of mild stability experienced over the last 10,000 years, the period known as the Holocene. Yet it is during this period of climatic stability that the entirety of human civilisation has developed and which set the conditions to which our agricultural systems, ports and cities are all adapted.

As a result of man-made emissions the planets average surface temperature is now ~0.8 degrees Celsius warmer than it was in pre-industrial times. Due to time lags in the climate system it is estimated that even if we stabilised atmospheric CO2 at its current concentration we would still see at least another 0.6C of warming before the earth reached equilibrium [[v]]. Despite all this we are continuing to add more CO2 into the atmosphere at an accelerating rate. We have failed to act on the best scientific advice and as a result we are now facing “a period of consequences.”

Scientists’ increasing alarm

This is an emergency and for emergency situations we need emergency action
this extraordinary statement was uttered by Ban Ki-Moon, Secretary General of the United Nations [[vi]]. Yet it is perhaps even more alarming that the claim strikes the same tone as normally staid scientists; such as Prof. James Hansen (recently retired from his role as NASA’s foremost climatologist and director of the Goddard Institute for Space Studies) who has said himself that "we are in a planetary emergency" [[vii]]. I could equally well quote the similar views of other renowned scientists such as Prof. Lonnie Thompson, director of the Byrd Polar Research Centre, who has said that “Virtually all of us are now convinced that global warming poses a clear and present danger to civilization.” [[viii]]. However this view, which is common amongst scientific circles, is rarely discussed in the public realm.

The sad truth is that the scientific evidence is looking far bleaker now then even just a few years ago. Prof. Sir. John Houghton, former co-chair of the IPCC, recently wrote of how “climate change is accelerating more rapidly and dangerously than most of us in the scientific community had expected or that the IPCC 2007 Report presented” [[ix]]. I shall now briefly examine why it is that the IPCC’s reports have often understated the risks and then overview the recent evidence of current and future climate impacts.

The IPCC has been tasked with assessing the evidence that the planet’s temperature is increasing and whether mankind is responsible, and on both these counts it has been able demonstrate a watertight case that it is heating and that we are the culprits [[x]]. The level of scientific consensus that has emerged is now overwhelming and is a testament to the procedures and structure of the IPCC. Yet the very nature of that consensus building exercise, that is so useful at establishing the veracity of key facts, tends to lead to conservatism when it comes to making predictions about future scenarios. The IPCC is a final stage review process and therefore lags behind the most recent developments in the scientific literature, which in turn lags behind the cutting edge of the field due to the time it takes for work to be sent out to peer-review.

Another important point to bear in mind is that climate scientists have been embroiled in the vicious public debate over climate science and consequently have tended to be reticent to raise their heads above the parapet. This has led to a tendency to try to appear more than reasonable and avoid making what appear to be alarming statements. Prof. Sir. Robert Watson, another former co-chair of the IPCC, exemplified this position clearly at a meeting in San Francisco in December 2012 “We have to be very careful. If we ever have a strong statement that’s later proved to be wrong, we would lose all credibility as a scientific community… I think we should always be slightly on the side of being conservative. Otherwise we are going to get ripped apart by climate-deniers even if we make the most simple mistake...” [[xi]]

This phenomenon has been dubbed “erring on the side of least drama” by historian of science Keynyn Brysse and her colleagues who in a recent paper published in the journal “Global Environmental Change” wrote that:

“In attempting to avoid drama, the scientific community may be biasing its own work - a bias that needs to be appreciated because it could prevent the full recognition, articulation, and acknowledgment of dramatic natural phenomena that may, in fact, be occurring” [[xii]]

Indeed, another recent study published in the same journal, describing a survey of recent papers on climate science, found that new scientific reports were twenty times more likely to have results which told of outcomes worse than the consensus compared to outcomes which were better. The authors concluded:

“…if reporters wish to discuss “both sides” of the climate issue, the scientifically legitimate “other side” is that, if anything, global climate disruption may prove to be significantly worse than has been suggested in scientific consensus estimates to date” [[xiii]]

So what are the new findings of the science suggesting that things are worse then expected?

The Arctic Sea Ice is melting far faster than predicted:

In September 2012 the Arctic sea ice reached it’s lowest ever summer minimum extent; smashing through the previous record, which had only lasted since 2007 [[xiv]].This continued and dramatic decline now means that the ice is melting far faster than had been predicted. "It is a greater change than we could even imagine 20 years ago, even 10 years ago" says Dr. Kim Holmen, Director of the Norwegian Polar Institute [[xv]]. The speed of the decline of the sea ice extent lies far outside of even the most pessimistic models that the Intergovernmental Panel on Climate Change (IPCC) presented in their fourth assessment report in 2007. As is shown in Figure 2:

Figure 2 - arctic sea ice extend over time

Figure 2. Comparison of observed decline of sea ice extent (red) against model projections form the IPCC’s 4th assessment report. [[xvi]]

The situation is actually far worse than is even shown in the above graph that only shows sea ice extent. Far more important is the September sea ice volume (area multiplied by thickness), which has declined by over 75% since the 1980’s.

The following graph (Figure 3) shows the decline in sea ice volume

Figure 3 decline in arctic sea ice volume over period 1979-2013

Figure 3. Decline in Arctic Sea ice volume over the period 1979-2013 with an exponential extrapolation. [[xvii]]

Some scientists now think that it is likely that before the end of this decade Arctic sea ice will have melted out completely in September. For instance, Sea ice expert Prof. Peter Wadhams from the University of Cambridge puts it thus; “The fall-off in ice volume is so fast that it is going to bring us to zero very quickly. 2015 is a very serious prediction and I think I am pretty much persuaded that that's when it will happen” [[xviii]]

Others still think that this point will be reached slightly later. Prof. Mark Serreze, director of the National Snow and Ice Data Center, says that “we may lose the summer ice cover as early as 2030…. This is in itself much earlier than projections from nearly all climate model simulations.” [[xix]] Either way almost all arctic sea ice experts now agree that the arctic sea ice has entered ‘a death spiral’.

The sea ice will continue its annual cycle of regrowth in winter and melting in summer, but there will be longer and longer periods of completely ice free conditions in the Arctic. This should be incredibly troubling to all of us as the sea ice acts as a giant mirror, reflecting most of the solar radiation in the summer back into space, whereas the dark oceans absorb the radiation thus adding to global warming and to further melting of the ice.

The melting of summer Arctic sea ice has now been linked to a series of extreme weather events driven by resultant changes to the jet stream, such as the massive 2010 Russian heat wave and the Pakistani floods of the same year [[xx], [xxi]]. It is also likely the cause of the extreme rainfall and flooding we witnessed in the U.K. in summer 2012 (which reduced wheat harvests to their lowest level since the 1980s, and the potato crop at its lowest since 1976. [[xxii]]).

Sea levels are rising faster than predicted

A recent study found that sea levels are already rising 60% faster than the IPCC predicted [[xxiii]]. The difference is in large part due to the far greater than anticipated melting of the Greenland and Antarctic ice caps; both are now shrinking at an accelerating rate. The Greenland ice sheet is now melting over five times as fast as it was in the early 1990’s.

Many glaciologists now think that, without dramatic cuts to greenhouse gas emissions, average sea levels will likely rise by a meter by the end of the century and perhaps by as much as two meters [[xxiv]]. There is also the daunting possibility that the West Antarctic ice sheet could collapse, as it has done on many occasions in the past. Were this to occur it would result in sea levels rising considerably faster, but the point at which this will occur is still as yet unknown.

Figure 4 shows the results of a recent survey of the opinions of ninety experts who are studying sea level rise for two different future emissions scenarios. It suggests that on average they expect sea level to rise by considerably more than was predicted in the latest IPCC AR5 estimates (which were themselves increased substantially above those in AR4), showing once again a tendency for the consensus reports to be conservative.

Figure 4 - sea level rise prediction to 2100 according to expert opinion

Figure 4. Sea level rise projections to 2100 according to expert opinion. Red = business as usual high emissions scenario. Blue = drastic reductions in emissions. The bars at the sides show the IPCC AR5 projections for the same scenarios. [[xxv]]

If sea levels do rise by a meter by 2100 then Prof. Stefan Rhamstorf, of the Potsdam institute for climate science, who was an author on the above study, says that this “could raise the frequency of severe flooding for New York City from once per century to once every three years.” [[xxvi]] Of course many other coastal cities around the world, including Amsterdam, Bangkok, Dakar, New Orleans, Miami, Mumbai, Shanghai etc., would also be highly threatened.

Whole countries would be severely affected, for example projections by the IPCC indicate that a sea-level rise of one meter would inundate up to 20% of Bangladesh’s land area and displace 14% of the total population. Large parts of Vietnam would also be badly hit; in particular rice paddies could be exposed to salt water infiltration which would greatly reduce yields, and is a significant global concern given Vietnam’s position as currently the world’s leading rice exporter.

CO2 emissions have been towards the IPCC’s “worst case” scenario:

As I pointed out earlier CO2 emissions have grown exponentially over the past twenty years. Worse, the rate of increase has actually been accelerating. Whilst global emissions had grown at an average rate of ~2.7% per annum for the past 100 years, since 2000 they have grown at a rate of about 3.5% per annum.

It is clear to see from Figure 5, which compares the rate of emissions growth to the various scenarios looked at by the IPCC that we are currently following the worst case examined. The X’s denote the observed rate of emissions growth over the relevant time periods for the each of the sets of scenarios looked at by the IPCC.

Figure 5 - observed growth rates of carbon dioxide emissions in different IPCC reports

Figure 5. Observed growth rates of carbon dioxide emissions compared to different scenarios used in the IPCC reports. [[xxvii]]

According to the International Energy Agency (IEA) the trajectory that we’re on puts us on course for a devastating 6 degrees C of warming by 2100. [[xxviii], [xxix]].

I shall return later to highlight the scale and urgency of the challenge required to reduce CO2 emissions to a level that would limit temperatures to a (still dangerous but perhaps bearable) level of 2 degrees C.

Heat & weather extremes are happening more frequently than predicted:

It is likely that the way most people will initially experience climate change impacts is through extreme weather events. In fact we have already witnessed dramatic rises in such events. For example heat extremes during summer compared to period 1950-1980 have increased dramatically. The shift in the distribution of heat extremes can be seen in Figure 6: 

Figure 6 - temperature distribution 1950-1980

Figure 6. Showing how the distribution of summer temperatures has shifted compared to a 1950-1980 baseline. We are now seeing many more extreme hot days.

This means we are now seeing far more heat extremes. We have in effect loaded the climate dice - or to put it another way we now have weather on steroids. So much so that we are seeing already (with only 0.8 degrees C of warming) that a “hot extreme, which covered much less than 1% of Earth’s surface during the base period [1950-1980], now typically covers about 10% of the land area.” [[xxx]]

The fact is that all weather events are now affected by climate change. As Prof. Kevin Trenbreth notes in an excellent paper on how to broach the question of the causality of weather events: “The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.” [[xxxi]]

One can, however, usefully talk in terms of probabilities and carry out attribution analyses in which climatologists calculate how much more likely an event is given climate change than it would have been in the natural climate. The extreme heat wave over Europe in the summer of 2003 is one of the events climatologists have analysed this way. They found that "it is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude." [[xxxii]]

Other events have also been ascribed to climate change in this way, for example, the flooding in the south west of England in autumn 2000 - which was between two and three times as likely to have happened because of global warming. [[xxxiii]]. Another is the Russian heat wave in 2010, which led to massive fires and the loss of ~40% of that nation’s wheat harvest. It is now estimated by scientists that the local warming trend in Russia “has increased the number of records expected in the past decade fivefold" [[xxxiv]]. (Indecently, it is thought that Russia’s subsequent food embargo was one of the key factors that led to the food riots at the start of the Arab Spring [[xxxv]]). The National Oceanic Atmospheric Administration in the U.S. also recently published findings that state that the extreme 2011 drought in Texas was 20 times more likely to occur due to climate change! [[xxxvi]]

Looking into the future we are likely to see many more heat records being broken. By 2040 it is expected that we will be seeing a ratio of 12:1 of heat records compared to cold ones! As is shown in Figure 7:

Figure 7 - observed record ratio of extreme weather

Figure 7. Observed record ratio (the increase in the number of heat records compared to those expected in a world without global warming) for monthly heat records as it changes over time (thin red line is annual data, thick red line smoothed with half-width 5 years). This is compared with predictions from a simple stochastic model based only on the global mean temperature evolution (blue line with uncertainty band directly comparable to the smoothed red curve) [xxxvii]

An author on this study points out that this is actually even worse than it sounds because, “to count as new records, they actually have to beat heat records set in the 2020s and 2030s, which will already be hotter than anything we have experienced to date” [[xxxviii]]

If we look at Europe we could expect to see far more dangerously hot days where the temp is over 35 degrees C in the day and over 20 degrees C at night. In particular Southern Europe, the Mediterranean and the Balkans will be very badly affected. See the map in Figure 8 for details (and this isn’t even for the worst case emissions scenario).

Figure 8 - maps show changes in extreme temperture for two future periods

Figure 8. Maps show changes in extreme temperature for two future periods, relative to 1961-1990. Extreme temperatures are represented by the combined number of hot summer (June-August) days where the maximum temperature exceeds 35 degrees C and night time temperature exceeds 20 degrees C. All projections are using the IPCC SRES A1B emission scenario for the periods 1961-90, 2021-2050 and 2071-2100 [[xxxix]].

The exceptionally hot summer temperatures in Western Europe in 2003 (which was responsible for the deaths of up to 70,000 people, massive wildfires and large damage to agriculture [[xl]]) will be the average summer temperature by the 2040’s and below average by the 2060’s [[xli],[xlii]]. Likewise, the extremely hot temperatures seen in America in 2012 could be the average temperature for that country in the next 10-30 years [[xliii]].

If we look at an analysis of extreme temperatures in 2100 (compared to the twentieth century for the United States) of the number of days which see temperatures reach over 100 degrees F (~38 degrees C). We can see (Figure 9) that under a business-as-usual scenario there are expected to be as many extremely hot days across most of the country as there are were in the Arizonan desert as recently as 1961-79!

Figure 9 - number of days expecvted over 100 degrees F in 2100

Figure 9. Number of days expected to be over 100 degrees F (38C) in 2100 compared to 1961-79 under a business as usual (A2) scenario.[xliv

If global average temperatures were to rise by 4 degrees C, then work by the Hadley centre suggests that on the hottest days of the year, we could expect to see an additional 6 degrees C or more in China, 8 degrees C in Western Europe and as much as 10 degrees C in New York [[xlv]]. At those kinds of temperatures cities would cease to function as transport and buildings overheat, hospitals swell with patients suffering from heat stress. Blackouts could occur as increases in cable resistance and surging demand for cooling cause electricity grids to fail. Crops would be devastated.

As the temperature of the planet changes so does it’s water cycle, which is now turning over at a faster rate [[xlvi]]. A recent study has shown that, as a result, rainfall intensity worldwide has already been observed to have increased by about 23%. The authors note “that the risk of extreme precipitation events due to global warming is substantially greater than that estimated by the climate models.” [[xlvii]].

Finally, warmer and moister atmospheric conditions lead to more frequent and intense storms and hurricanes. A recent paper in Proceedings of the National Academy of Sciences notes that extreme storm surges on the scale of the one following Hurricane Katrina in New Orleans are now twice as likely to occur as they were during the 20th century, and with 2 more degrees C of warming they will be up to 10 times as likely! [[xlviii]]

All these extreme weather events severely threaten agricultural yields and food security. Reports by Oxfam state that by 2030 the price of wheat in real terms will be ~120% higher than 2010, for maize the increase could be as much as 180%! [[xlix]] With a large part of this increase being a direct result of climate change, as is shown in Figure 10 below:

Figure 10 - real food price changes predicted for 2030

Figure 10. Real food price changes predicted for 2030 relative to 2010. Solid bars are the baseline; dashed bars include climate change related costs [ xlviii ]

Awful as that will be in terms of the humanitarian costs it will bring, this too has the potential of being far worse. Subsequent analysis by Oxfam to examine the effects of a shock to food prices similar to that experienced as a result of last years drought in the U.S. bread basket could see prices increase by an additional 33% for wheat and 140% for maize. That is to say there would be a three fold increase in wheat prices and a 6.5 fold increase in corn prices compared to 2010! [[l]]

We are already beginning to see detectable effects of climate change impacting on the world’s most vulnerable. Just earlier last year, for the first time, climate change was directly implicated in the humanitarian disaster in Sudan [[li]]. Questions are also being asked about the links between climate change and the extreme drought which struck Syria causing huge internal displacement and adding huge stress to that country just prior to the outbreak of the ongoing civil war in 2011 [[lii], [liii], [liv]].

The Oceans are acidifying:

As CO2 dissolves in water it lowers the waters pH. The Oceans are now 30% more acidic than they were before the industrial revolution. This phenomenon, dubbed global warming’s “equally evil twin”, spells major problems for marine life. However it wasn’t addressed at all in any of the first three IPCC reports and was only briefly discussed in the fourth. We now expect that if we were to stick to a business-as-usual pathway then by the end of the century the seas would reach a level 150% more acidic then they were prior to industrialisation [[lv]].

As the increased acidity removes carbonate ions in the water, which are used by many types of marine organisms such as Corals, Crustaceans, Molluscs, and various vital types of plankton species to grow their shells and skeletons, we can expect that there will be major negative impacts on marine food chains, which are the basis all our fisheries [[lvi]].

Corals will be particularly badly affected, as their thermal sensitivity already means that they will be struggling to cope with the heat wave events caused by even just 2 degrees of warming, ocean acidification could well be to be the straw that breaks the camel’s back [[lvii]]. We are perilously close to losing this wondrous storehouse of biodiversity, whose structure functions as the breeding grounds for many of the world’s fisheries, on which so millions of people’s livelihoods depend.

The risk of feedbacks:

The final crucial factor that has been missing from IPCC predictions to date is the possibility of triggering positive feedbacks that add to the warming. We already touched on the melting of the Arctic ice cap, which is an example of such a feedback coming into play much earlier than expected.

Another very important feedback, lacking from IPCC models, is the melting of permafrost, which essentially is frozen soil that holds vast stores of additional

carbon deposits [[lviii]]. More brand new results suggest that we may reach the tipping point at which these stores begin to be released as greenhouse gases after only 1.5 degrees C of warming [[lix]], this would then add to the increase in the planets temperature, but scientist are currently unable to tell us how large an additional increase this will be [[lx]].

Other potential key tipping points, for which the trigger point is as yet unknown, but become more certain to occur as temperatures continue to rise, include disruption of the Indian monsoon, the collapse of the West Antarctic ice sheet, and the dieback of the amazon rainforest.

The challenge of two degrees:

It is to try and avoid the huge risks associated with these tipping points that we have an international agreement to limit global temperature rise to below 2 degrees C. Unfortunately because of the recent findings (some of which I have outlined above) the risks upon which that decision was made now look considerably worse, you could say that 1 degree C is the new 2 degrees C [[lxi]]. See Figure 11 comparing the change in the perceived risks from climate change:

Figure 11 - updated reasons for concern

Figure 11. Updated reasons for concern. A visual representation for the risks of different categories of climate impacts associated with different temperature increases. The set on the left appeared in the IPCC third assessment report in 2001, the set on the right was an update using the same methodology carried out in 2009. [[lxii]]

I hope it is clear from the above, just how crucially important it is to limit global warming to no more than 2 degrees C above pre-industrial temperatures. Yet, as I pointed out above, even the International Energy Agency thinks we are on course for 6 degrees C of warming by the end of the century!

Many experts feel that even 4 degrees C by 2100 would be beyond our capacity to adapt. Prof. Kevin Anderson, former director of the Tyndall centre for climate change research, puts it this way: “…there is a widespread view that a 4°C future is incompatible with any reasonable characterisation of an organised, equitable and civilised global community. A 4°C future is also beyond what many people think we can reasonably adapt to. Besides the global society, such a future will also be devastating for many if not the majority of ecosystems.

Beyond this, and perhaps even more alarmingly, there is a possibility that a 4°C world would not be stable, and that it might lead to a range of ‘natural’ feedbacks, pushing the temperatures still higher” [[lxiii]].

At the end of 2012 the World Bank issued a report titled “Turn down the heat: Why a 4°C Warmer World Must be Avoided” which concluded similarly that:

 “…there is also no certainty that adaptation to a 4°C world is possible. A 4°C world is likely to be one in which communities, cities and countries would experience severe disruptions, damage, and dislocation, with many of these risks spread unequally. It is likely that the poor will suffer most and the global community could become more fractured, and unequal than today. The projected 4°C warming simply must not be allowed to occur” [[lxiv]]

Given the profound risks we are facing it seems incredible that more is not being done to reduce our emissions. There are many reasons as to why we aren’t acting, perhaps the key one being the massive disinformation campaign being carried out by vested interests [[lxv], [lxvi]]. Leaving that aside, I shall now address what I believe are three common misunderstands of the science that are contributing to inaction.

Nonlinearities and time lags:

As discussed above many of the impacts of climate change are non-linear. The consequences of a 4 degree C warmer world wouldn’t just be double those of a 2 degrees C warmer world, as is sometimes mistakenly assumed, they would be far, far worse. However, because these nonlinearities mean that climate impacts will tend only to worsen gradually at first, we risk being led into a false sense of security before the impacts start hitting us far more rapidly later on. The risk of triggering positive feedback mechanisms could make these nonlinearities worse as different feedbacks accelerate each other. Climate impacts will also be occurring simultaneously and will likely act synergistically, such that the combined effect of the impacts will be greater than the sum of all the impacts independently. We must also be aware of the possibility of their being ‘unknown unknowns’; risks we have not identified yet which may lie ahead.

The other hazard is the time lags in the climate system, as I mentioned earlier we would expect to see a further 0.6 degrees C of warming even if we instantaneously stabilised atmospheric CO2 concentrations. These time lags mean we haven’t yet felt the impacts of our past and current actions, and this could again lead us to adopt a false sense of security. Sea levels, for example, will continue to rise for a long while after we stabilise CO2 concentrations.


The second misunderstanding, related to that above, is the idea that climate change and climate impacts will be reversible. Recent studies have shown that, far from this being the case, climate change would in fact be largely irreversible for at least one thousand years, meaning that the actions of those alive today will have repercussions lasting for tens of generations to come [[lxvii]]. This perhaps counter-intuitive result is because the Oceans are acting as a massive heat reservoir, which have stored up heat very quickly over the last one hundred years. Even if we ceased emissions today, the oceans would only very gradually lose that heat keeping atmospheric temperatures high for centuries.

Another factor that adds to the irreversibility is the possibility of the tipping points in the climate system discussed above. For example, were large parts of the ice sheets to melt, such as the collapse of the West-Antarctic shelf, it would take tens if not hundreds of thousands of years for them to re-establish and sea levels to subside.

The urgency of the situation; or why long-term targets are meaningless:

Many people feel that we have plenty of time to reduce carbon emissions and that the threat is a long way off – they could not be more wrong. The most important point here is to appreciate that we are dealing with a stocks and flow problem. The best analogy is that of a bathtub. Imagine we are filling a bath. What matters to the level of the bathwater is the difference between the rate water flows in and the rate it flows out. So long as the inflow exceeds the outflow the bath will overflow – we will have exceeded our target!

Now the atmosphere is that bathtub into which we are pouring CO2 far faster than it leaves (a molecule of CO2 typically stays in the atmosphere for 100 years or more), as such the cumulative emissions are amassing, and the concentration in the atmosphere is steadily increasing. This is the crucial point as it is the cumulative emissions that determine the planets final temperature, not the rate at which we are emitting greenhouse gases at any given date in the future.

Once we grasp this point we realise that, if we wish to stay below 2 degrees C of warming, we have a fixed budget of CO2 emissions that we can emit between now and 2050. Reducing emissions slightly won’t solve the problem as global warming won’t stop getting worse until we reduce CO2 emissions to a rate which is less than CO2 is being removed from the atmosphere. The longer we wait before the world peaks its emissions, then the faster we need to cut emissions after that peak in order to stay within our cumulative emissions budget.

The diagram in Figure 12 illustrates the point, bear in mind that it is the area under each curve that matters:

Figure 12 - cumulative emission budget for 67% chance of staying below 2C
Figure 12. Three scenarios with a cumulative emissions budget for a 67% chance of staying below 2 degrees C. The different coloured lines represent different peak emissions dates, green is 2011, blue is 2015, red is 2020. The longer we wait before reducing emissions the faster we must then reduce emissions in order to remain within the same emissions budget. The area under each curve is the same i.e. the same total amount of carbon has been emitted. [[lxviii]]

This completely changes how we must approach this problem as we can no longer think in terms of long-term targets, we must instead urgently aim to peak and then reduce emissions, as the longer we wait the harder and more costly the change will be.

What I haven’t mentioned yet is that because of uncertainties in our understanding, the science can only offer probabilistic carbon budgets. We can make a statement such as this; to have an 80% chance of staying below 2 degrees we can only afford to emit 886 Gigatonnes of carbon between 2000 and 2050 (we’ve already burnt through 321 Gigatonnes) [[lxix]]. It strikes me as important to point out that an 80% chance is worse odds than playing Russian Roulette with a six shooter! Of course if we’re prepared to accept worse odds still then this then budget gets bigger. A 1,440 Gigatonne budget between 2000-2050 would give a coin flip’s (50:50) chance of staying under 2 degrees C [[lxx]]. The U.K. Government has currently adopted a much larger carbon budget that only gives us only a 37% chance of staying below 2 degrees! [[lxxi]].

The importance of the concepts of carbon budgets cannot be overstated. It shows us that we must adopt an urgent and radical approach to dealing with Climate Change, we cannot delay action any further. It also makes plain that the idea of long-term reduction targets is shown to be scientifically meaningless, but they are comfortably outside of current politicians’ time in office.

One recent and credible estimate from members of the Tyndall centre suggests that to do its equitable share for a 63% chance of staying under 2 degrees C the U.K. must begin cutting emissions at a rate of almost 8-10% per annum. That is an ~40% reduction on 1990 emission levels by 2015, a reduction of ~70% by 2020-2025 and ~95% reduction by 2030-2035 [lxxi]. The implication of the need for such swift reductions in fossil fuel use is that they can only be achieved (in the short term at least) by reductions on the energy demand side, as there simply is not enough time to build replacement green energy supplies. Demand side reductions will require large-scale social and behavioural changes as well as the adoption of highly efficient end use technologies.

One other crucial fact follows from the concept of a carbon budget and that is that we can compare the size of the budget to the size of our known fossil fuel reserves. If we do this then we find that, if we want an 80% chance of staying below 2 degrees C, we have five times the necessary fossil fuel reserves [[lxxii], [lxxiii]]. Even the IEA admit that for only a 50% chance we would still need to leave two thirds of our available fossil fuel reserves in the ground, unburned! [[lxxiv]]. It is according to the logic of this argument that we can easily claim that it is entirely incongruent for our Government to be thinking of allowing the development of shale gas in the U.K. as the World already has far more fossil fuels then it can safely use.

The scale of this challenge is enormous, and has led many leading policy experts and climate scientists to declare that this target is impossible in the current political context. Prof. Sir Bob Watson, former co-chair of the IPCC and chief scientist to DEFRA, recently stated his opinion that the "2°C target is largely out of the window.” [[lxxv]]. However, we have to really consider the alternative scenario here; can we in any meaningful sense say that living with the consequences of a 4 degree C warmer world is any less impossible? Prof. Hans Schellnhuber, director of the Potsdam institute and an advisor to the German Chancellor once pointed out that “Political reality must be grounded in physical reality or it's completely useless”. [[lxxvi]]

Quoting a new Pricewaterhouse Coopers report “Too late for two degrees?” on the matter we can say confidently that “business-as-usual is not an option” [[lxxvii]]

Our choice

If we keep burning fossil fuels then by 2100 the temperature of the planet will be 4-6 degrees Celsius hotter than it was in 1900 (Figure 13). This change is similar in scale to that between the depth of the last ice age and the subsequent interglacial warm period. But this change will have happen on a far shorter time scale. As I’ve tried to make clear, scientists are becoming increasingly alarmed that observations repeatedly suggest that the damaging impacts of climate change are coming sooner than expected. Failure to take action to reduce emissions will mean that the consequences of climate disruption for humanity and the planets ecosystems will be devastating, there is no guarantee that we can adapt to such a shift in our climate.

However, all is not lost. The actions and decisions of our generation over the next decade will determine which pathway we will follow and which future will come to pass. It is still physically and technically possible to hold the temperature increase of our planet to two degrees Celsius if we begin to take radical action now. Every year of delay makes this harder and more costly to achieve.

Figure 13 - temperature projections going out to 2100

Figure 13. Temperature projections going out to 2100. The black line shows the historical temperature record, the red shows the business as usual pathway the blue the radical mitigation pathway needed to stabiles at 2 degree C, the shading represents uncertainty in the science [[lxxviii]]. I’ve added three green-bands to represent different generations. The yellow-band represents the influence our decisions could have on the conditions experienced by future generations. (Modelled on a graph by Prof. Lesley Hughes)

We are facing a crisis so large, that it is no exaggeration to say that it could determine the fate of civilization itself. Yet, it is a crisis of our own making and as such we are in the remarkable position of being able to take actions to avert the worst effects, if we so choose.

To be persuaded to make the necessary and appropriate changes the public needs to be informed of the scale of risks and the challenges ahead. It is my opinion that political and community leaders are crucial to achieving this. We elect politicians to look out for the best interests of society, and to make difficult decisions on our behalf. To ignore this issue either for lack of public concern or because the challenge looks to be politically inconvenient, is an abdication of moral responsibility of the worst kind. All of us who are aware of the risks faced are culpable if we do not do act to do our upmost to avert the oncoming disaster. The fates of millions for generations to come are held in our hands. Reality will not wait for us, we cannot change the laws of physics, but we can change our laws and our behaviors. I refuse to believe that a civilization that has abolished slavery, put men on the moon and wiped out the scourge of Small Pox cannot rise to this challenge. I fully recognize that the challenge facing us is undeniably immense, and will likely take a restructuring of our economy and society similar to the scale of the changes that took place during World War Two. But did our forbears shirk their obligation to fight the rise of fascism? NO! Our then leaders took on the challenge and took the country with them on to win.

And so I finish as I began with a quote from Sir Winston Churchill for you all to ponder:

"It is no use saying, 'We are doing our best.' You have got to succeed in doing what is necessary.”

I urge you all to inform yourselves and to engage with others to get people talking about what is at stake. Reduce your ecological footprint and increase your political footprint. Join the ranks of those fighting for climate justice – let us unite and save our future!

Dr. Aaron Thierry

May 2014



[xxxiii] http://www.nature.com/nature/journal/v470/n7334/full/nature09762.html

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