Climate Change

'Global warming' is not a very satisfactory term for what has been happening to our climate over the last one hundred years, for we have seen not only increasing temperatures but also more extreme weather, with worsening floods and droughts and rising sea levels.

'Climate change' isn't a very satisfactory term either, because the world's climate has always changed naturally and significantly over very long time scales, so you might be tempted to dismiss recent trends as something normal that we don't need to worry about.

Whether you call it 'global warming' or 'climate change', the important thing to understand is that the world's climate has been changing unusually fast over the last one hundred years, and that much or all of this rapid change must therefore be caused by human activities such as deforestation and the burning of fossil fuels (oil, coal and natural gas). The burning of fossil fuels releases large amounts of CO2 into the atmosphere. CO2 is a 'greenhouse gas', i.e. a gas that traps some of the heat radiation that would otherwise be emitted from the earth into space. Methane is another greenhouse gas, about 20 times more potent than CO2, but fortunately there is much less methane than CO2 in the atmosphere. Since the industrial revolution began in 1750, CO2 levels have risen by more than 30% and methane levels have risen more than 140%. The concentration of CO2 in the atmosphere is now higher than at any time in at least 800,000 years.

This chart, the famous 'Keeling curve', shows how the concentration of CO2 in the atmosphere has evolved since 1965. The annual rise and fall is caused by leaves growing on deciduous trees in the northern hemisphere in the spring and summer (taking carbon out of the air) and then falling and decomposing in the autumn and winter.

The following chart shows how the world's average temperature has risen since 1880 (source: NASA GISS):

The Earth's average temperature has risen about 1 degree Celsius in the last 100 years. That doesn't sound very much, but scientists tell us that a temperature rise of 2 degrees or more would almost certainly be dangerous, and that we need to limit the temperature rise to 1.5 degrees (since 1850) to be on the safe side. There is nothing magical about these numbers and they do not imply that humans will become extinct if the temperature rises 2°C, only that such rises will cause much damage and the greater the temperature rise, the more damaging climate change will be. For a good introduction to climate change, see this BBC article (be sure to watch the videos too). For a more thorough introduction, see this excellent guide by the Economist magazine. Also watch Al Gore's documentary 'An Inconvenient Truth'. It was made 13 years ago but the science is still considered to be quite accurate. It is available in France on Netflix.

For several decades there has been an awareness that rapid climate change is occurring and for several decades and at the United Nations Conference on Environment and Development held in Rio de Janeiro in 1992, the United Nations Framework Convention on Climate Change (UNFCCC) was adopted with the aim of stabilising greenhouse gas concentrations in the atmosphere at a sustainable level and thus counteracting serious consequences. It entered into force in 1994. The signatory states meet at regular intervals at the so-​called COPs (Conference of the Parties) to agree on further action in climate protection. In 1997, this meeting was held in Kyoto in Japan, during which the "Kyoto Protocol", the first document with legally binding obligations for limits and reductions, was adopted by the ratified countries. The period of applicability was set for the years 2008 to 2012 (obligation period 1) and 2013 to 2020 (obligation period 2).

In order to be able to maintain the international climate protection process after 2020, a new climate agreement was required. This was adopted in 2015 at the COP in Paris as the "Paris Agreement", which, for the first time, included a specific target for limiting global warming at a level of at least 2°C below the pre-​industrial level of 1750 and to limit the increase to 1.5 °C, since this would substantially reduce the risks and effects of climate change. . The most important difference between the Kyoto Protocol and the Paris agreement is that developing countries are submitting pledges under the Paris agreement to reduce emissions. They had no emissions-reduction (mitigation) obligations under Kyoto Protocol.

Under the Paris Agreement, each country must determine, plan, and regularly report on the contribution that it undertakes to mitigate global warming. No mechanism forces a country to set a specific target by a specific date, but each target should go beyond previously set targets. In June 2017, U.S. President Donald Trump announced his intention to withdraw the United States from the agreement. Under the agreement, the earliest effective date of withdrawal for the U.S. is November 2020, shortly before the end of President Trump's current term. In practice, changes in United States policy that are contrary to the Paris Agreement have already been put in place.

It quickly became apparent that the Paris Agreement would fail to limit temperature rises as hoped. A pair of studies in Nature said that, as of 2017, none of the major industrialized nations were implementing the policies they had envisioned and that they had not met their pledged emission reduction targets, and even if they had, the sum of all member pledges (as of 2016) would not keep global temperature rise "well below 2°C". According to UNEP the emission cut targets in November 2016 will result in temperature rise by 3 °C above pre-industrial levels, far above the 2 °C of the Paris climate agreement. In addition, a 2016 MIT News article concluded that the Paris Agreement would only reduce temperatures in 2050 by 0.1°C compared to taking no action, and by only 0.6 to 1.1 degrees in 2100 compared to taking no action, meaning that under all scenarios, warming would be at least 3.0 °C by 2100.

A report by the IPCC (Intergovernmental Panel on Climate Change), which the U.N. climate science body released Oct. 8, 2018, revealed that the best path to limiting warming to an increase of 1.5 C by 2100 involves cutting net human carbon dioxide (CO2) emissions 45% by 2030 and then cutting emissions further to net zero by 2050. See this excellent article: 'Are We Really Running Out of Time to Stop Climate Change?'

Al Gore did what he could to raise public awareness of the climate change crisis with his 2006 film 'An Inconvenient Truth' (available on Netflix in France) and, in 2017, 'An Inconvenient Sequel', but it is a 16 year old girl, Greta Thunberg, who is currently inspiring protests around the planet. Here she is, aged 15, sitting outside the Swedish Parliament in August 2018. This was the first school strike against climate change, and Greta was all alone.

Barely a year later, on Friday 20 September 2019, around four million people in thousands of cities and towns around the world protested against climate change. Many of the protesters were young people, for they will be more affected by climate change than older people. The protests were also notable for where they didn’t take place: China, which is currently the biggest greenhouse gas emitter of all. Watch Greta Thunberg make an 11 minute TED speech:

On Monday 23 September, the same day that Russia at last ratified the 2015 Paris climate agreement and that my students and I began our climate change project, world leaders gathered for the annual United Nations general assembly aiming to inject fresh momentum into efforts to curb carbon emissions. But little progress was made at the summit. China said absolutely nothing new, India mentioned commitments made in the past, the US, Canada and Australia weren’t there (though Donald Trump dropped in briefly). Greta Thunberg WAS there and expressed her disappointment:

Donald Trump reacted to Greta's speech by mocking her, tweeting "She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!" Donald trump is not the only person to mock her. Famous French philosopher Michel Onfray goes further, commenting that she expresses little emotion and suggesting that she may be some kind of cyborg. In French:

Greta is seen as the 'messiah of the global warming movement' by some and as a demon by others. She is very young, just 16, so surely she is being manipulated? Who writes her speeches? This article says she writes her own speeches, but she has a network of contacts who advise her - including climate scientists and campaigners. This article gives more information on 'The Machine behind Greta Thunberg'.

Watch Greta propose a natural but only partial solution to the climate crisis, and see also here:

The Economist suggests that there is a problem with the idea that planting new forests is a good way of locking up carbon: often the new forests are planted with the idea of harvesting the trees every few years for financial gain, which causes the carbon to be released back into the atmosphere. Forests lock up carbon best if they are left undisturbed.

In the context of worldwide protests against rapid climate change, this is an excellent moment for us to do a school project on climate change, focusing especially on the scientific side.

To limit climate change, the most urgent need is to vastly reduce our reliance on burning fossil fuels. This is easier said than done! In fact that will be a HUGE challenge for developed countries, because we are strongly 'addicted' to fossil fuels. The world's GDP is very closely correlated with our energy use (mainly fossil fuels), a relationship known as the Garrett relation. Fossil fuels are used on a massive scale for making electricity, making plastics, powering industry, transport, heating, cooking and more. Drastically cutting fossil fuel use might require us to greatly modify our way of life and could lead to civil unrest. A foretaste of this has been seen in France, where a government attempt to apply a carbon tax to fuel triggered many months of protest by the 'gilets jaunes' and expensive concessions by the government. Reducing our reliance on fossil fuels could mean replacing them with other sources of energy, or it could mean reducing our energy consumption, for example by avoiding taking long flights when we go on vacation or heating our homes less in the winter.

It would be nice to be able to replace fossil fuels with renewable energy sources. Wind and solar power are renewable and affordable energy sources but have a huge disadvantage: they are intermittent. In order for us to be able to rely heavily on wind and solar we need to develop better energy storage systems, and we will do research on this with a special focus on battery technology since this is also relevant to electric cars.

Conventional nuclear power provides huge amounts of carbon-free, always-on electricity, especially in France, but has major problems of safety, cost and waste disposal. We will look at a promising new form of nuclear fission power plant called the molten salt reactor which uses thorium rather then uranium as fuel and should be cheaper, safer and less polluting that conventional fission power. See this introduction to molten salt reactors and also this one, but read the comments for the second one because the presenter makes a couple of errors, probably including the suggestion that the Uranium-233 made by the reactors could easily be made into atomic bombs. Also check out this web site. Perhaps we will also look at fusion power, which will be even safer and cleaner but which, some people say, will always be thirty years away.

Ultimately, it will be extremely difficult and painful to rapidly reduce our use of fossil fuels, so no doubt we will continue burning too much of it, which means we will also need to capture some from the atmosphere or from factory chimneys and then store it safely, a process known as carbon sequestration. It's already quite possible to capture carbon in the exhaust gases of electrical power stations that burn fossil fuels, but it's not cheap and power stations only account for about 25% of our CO2 emissions, with transport and general industry counting for much more. See here and here.

Some numbers

Human activities currently emit about 40 billion tonnes of CO2 per year or 4.6 million tonnes per hour or 1286 tonnes per second (this does not take into CO2 emitted in other ways, such as by volcanoes, nor does it take into account CO2 absorbed by the Earth e.g. by the oceans). Imagine that all of Africa is covered by forest. The CO2 that we emit would be equivalent to burning that much forest every 9 months (see here).

Check out the charts below, which come from the EPA (United States Environmental Protection Agency).

You can multiply the figures for carbon by 3.7 to get corresponding figures for CO2, since a molecule of CO2 is 3.7 times heavier than a carbon atom.

Climate Change Deniers

There are still a very small number of scientists who believe that the rapid climate change of the last 100 years is NOT largely due to human activities. They and some other people argue that climate change is normal or that it has not been 'proved' that the current rapid climate is largely due to human activities, and therefore we need not take action. This is stupid thinking. Even if there is only a small chance of some catastrophic event happening (which is not the case) it makes sense to try to reduce the risk of it occurring. There is only a small chance of you being badly injured in a car crash the next time you travel in a car, but you will of course wear your seat belt just in case. Another example: suppose NASA discovers tomorrow that there is a large asteroid heading our way and that there is a 10% chance of it inflicting catastrophic damage to the Earth. Would we do nothing? Of course not! We would never fail to act if were told that there is a 10% chance of catastrophic damage being inflicted in the Earth in this way. We would try to push the asteroid so that it cannot hit the Earth, or perhaps break it into tiny harmless pieces. So even if we thought that there is only a 10% chance that unmodified human activities would cause catastrophic climate change this century we should act, and scientists have a strong consensus that the probability is not 10%, but very high.

Nevertheless, it may be a good idea to look at the kind of arguments put forward by 'climate change deniers'. Quite often, it seems to me, climate change deniers miss the point, which is that global temperatures are rising much faster now than happened during climate variations in the past. It's easy to find on YouTube, for example, climate change denial videos such as these below. My advice: DO NOT WATCH THESE VIDEOS otherwise you may begin to doubt whether humans are really responsable for the rapid climate change that has been occurring for the last century..

  • rebuttals: 1 2 3
  • This geologist accepts that the climate is warming fast and that humans are largely responsible but says that CO2 levels now (we've gone from 270 ppm to 400 ppm since the industrial revolution began) are only about one sixth of the historical average value of 2600 ppm. He says that plants and animals thrived when CO2 levels were that high in the past, and can thrive again if we allow CO2 levels to rise way beyond today's levels. However, I don't think he addresses the problems of rising sea levels displacing millions of people or extreme weather etc.

Some of the arguments put forward by climate change deniers are refuted in this video:

Speaking of climate change deniers, we should perhaps give special mention to US president Donald Trump. The United States has produced more emissions than any country since the start of the industrial age, and now under Donald Trump, it is rolling back a suite of environmental regulations .

Watch two MIT graduate students talk for 15 minutes about their plans for a Waste Annihilating Molten Salt Reactor which will use waste from conventional nuclear plants to supply all the word's electricity needs for the next 72 years.

The bottom line

We must not forget that our use of fossil fuels is largely responsible for the huge advances that have been made since 1850 in developing countries. Our standard of living, wealth and life expectancies have all improved far more than would have happened had we not had plundered vast amounts of fossil fuels. See Why You Should Love Fossil Fuel (5 minute video). Hugely limiting our use of fossil fuels might mean that our quality of life would slip backwards, and it would also stop developing countries attaining the standard of living of developed countries, would be very unjust. It seems likely that people will not be willing to accept the huge costs and sacrifices that are necessary to limit climate change to tolerable levels, and carbon sequestration is also unlikely to be a good solution, due to the scale of sequestration that will be necessary. Say we manage to reduce our current CO2 emissions by 50% to 'only' 2.3 million tonnes per hour and that we want to use carbon sequestration to compensate for those emissions. According to my calculations, we would need to remove the CO2 from nearly 1 km3 of air per second, which is a vast amount. If we built 10 thousand sequestration plants around the world to achieve this, each one would have to process 4 000 000 m3 of air every 40 seconds, which is the volume of Wembley football stadium, one of the largest football stadiums in the world. I am not confident that this is possible.

What can I do to help?

This good BBC article stresses that we won't be able to solve the climate crisis with small, painless changes - there will be upheaval as major changes to our way of life will be necessary such as eating less meat and dairy, swapping cars for bikes, taking fewer flights, and ditching gas boilers at home. The article makes it clear that the UK intends to lead the world in fighting climate change, just as it led the world with the industrial revolution which actually caused the climate crisis.

This BBC page called 'Climate change: Where we are in seven charts and what you can do to help' is excellent.


On 25 September a major United Nations report was issued by scientists who met in Monaco. They say that climate change is devastating our seas and frozen regions as never before. Waters are rising, the ice is melting, and species are moving habitat due to human activities. The seas were once rising mainly due to thermal expansion, the way water expands when it is heated. But the IPCC says rising water levels are now being driven principally by the melting of Greenland and Antarctica. This new report says that global average sea levels could increase by up to 1.1m by 2100, in the worst warming scenario. "What surprised me the most is the fact that the highest projected sea level rise has been revised upwards and it is now 1.1 metres," said Dr Jean-Pierre Gattuso, from the CNRS, France's national science agency. "This will have widespread consequences for low lying coasts where almost 700 million people live and it is worrying." Read the BBC article.

On November 5 eleven thousand scientists warned of untold suffering due to the climate crisis.

On December 24 2019 the MIT Technology Review site published 'Our pathetically slow shift to clean energy, in five charts'. Here's one of the charts. It shows that even though renewables are growing for electricity generation, they are still dwarfed by fossil fuels. Even worse, it shows that despite our awareness that we need to leave fossil fuels in the ground, our use of coal and gas has never been so high and is still increasing!

Other factors

Climate change is affected by many factors, not all of which are mentioned in the introductory articles and videos proposed on this page. I've listed some other factors here.

Other links

For the latest news about climate change, follow the BBC's news feed:

BBC Briefing on energy (includes a 200 page PDF for UK energy use)

The Road to Clean Energy is a condensed version of the BBC Briefing on Energy. It's focused on the UK but is well written and comprehensive. It might take 30 minutes to read. It says that we have solutions for most of the sources of CO2, with the possible exception of aviation. Aviation is difficult to fix because it's not conceivable to fuel long flights with heavy batteries or heavy hydrogen cylinders, but this article says we can make aviation fuel from biomass or from CO2 captured from the air. It also says that air travel accounts for between three and five percent of the global CO2 emissions (7% for the UK) and those emissions are growing fast.

The Economist: Predicting the climatic future is riddled with uncertainty

Can we really replace fossil fuels with renewable energy? See this reality check on YouTube.