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Weather Patterns are Changing Radically on Earth
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years.
Global warming is the continuing rise in the average temperature of Earth's atmosphere and oceans.
Global warming is caused by increased concentrations of greenhouse gases in the atmosphere, resulting from human activities such as deforestation and burning of fossil fuels.
This finding is recognized by the national science academies of all the major industrialized countries and is not disputed by any scientific body of national or international standing.
It may be a change in average weather conditions or the distribution of events around that average.
Climate change may be limited to a specific region or may occur across the whole Earth.
The most general definition of climate change is a change in the statistical properties of the climate system when considered over long periods of time, regardless of cause.
Accordingly, fluctuations over periods shorter than a few decades, such as El Niño, do not represent climate change.
Glaciers are considered among the most sensitive indicators of climate change. Their size is determined by a mass balance between snow input and melt output.
As temperatures warm, glaciers retreat unless snow precipitation increases to make up for the additional melt; the converse is also true.
Glaciers grow and shrink due both to natural variability and external forcings.
Variability in temperature, precipitation, and englacial and subglacial hydrology can strongly determine the evolution of a glacier in a particular season.
Therefore, one must average over a decadal or longer time-scale and/or over a many individual glaciers to smooth out the local short-term variability and obtain a glacier history that is related to climate.
A world glacier inventory has been compiled since the 1970s, initially based mainly on aerial photographs and maps but now relying more on satellites.
This compilation tracks more than 100,000 glaciers covering a total area of approximately 240,000 km2, and preliminary estimates indicate that the remaining ice cover is around 445,000 km2.
The World Glacier Monitoring Service collects data annually on glacier retreat and glacier mass balance From this data, glaciers worldwide have been found to be shrinking significantly, with strong glacier retreats in the 1940s, stable or growing conditions during the 1920s and 1970s, and again retreating from the mid 1980s to present.
The most significant climate processes since the middle to late Pliocene (approximately 3 million years ago) are the glacial and interglacial cycles. The present interglacial period (the Holocene) has lasted about 11,700 years.
Shaped by orbital variations, responses such as the rise and fall of continental ice sheets and significant sea-level changes helped create the climate. Other changes, including Heinrich events, Dansgaard–Oeschger events and the Younger Dryas, however, illustrate how glacial variations may also influence climate without the orbital forcing.
Extreme Weather and Warming
Glaciers leave behind moraines that contain a wealth of
material—including organic matter, quartz, and potassium that may be
dated—recording the periods in which a glacier advanced and retreated.
Similarly, by tephrochronological techniques, the lack of glacier cover
can be identified by the presence of soil or volcanic tephra horizons
whose date of deposit may also be ascertained.
Past precipitation can be estimated in the modern era with the global
network of precipitation gauges.
Surface coverage over oceans and remote
areas is relatively sparse, but, reducing reliance on interpolation,
satellite data has been available since the 1970s.
Quantification of climatological variation of precipitation in prior centuries and epochs is less complete but approximated using proxies such as marine sediments, ice cores, cave stalagmites, and tree rings. Climatological temperatures substantially affect precipitation.
For instance, during the Last Glacial Maximum of 18,000
years ago, thermal-driven evaporation from the oceans onto continental
landmasses was low, causing large areas of extreme desert, including
polar deserts (cold but with low rates of precipitation).
The Girl who Silenced the World for 5 Minutes
In contrast, the world's climate was wetter than today near the start of the warm Atlantic Period of 8000 years ago.
Estimated global land precipitation increased by approximately 2% over the course of the 20th century, though the calculated trend varies if different time endpoints are chosen, complicated by ENSO and other oscillations, including greater global land precipitation in the 1950s and 1970s than the later 1980s and 1990s despite the positive trend over the century overall.
Similar slight overall increase in global river runoff and in average soil moisture has been perceived.
Climate conditions in the past provide evidence that
rising atmospheric carbon dioxide levels are associated with rising
global temperatures. Human activities, primarily the burning of fossil
fuels (coal, oil, and natural gas), and secondarily the clearing of
land, have increased the concentration of carbon dioxide, methane, and
other heat-trapping ("greenhouse") gases in the atmosphere.
An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, and a probable expansion of subtropical deserts. Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice.
especially people in positions of power – have invested a tremendous
amount of effort and time to get to where they are. They really don't
want to hear that we're on the wrong path, that we've got to shift gears
and start thinking differently."
–– David Suzuki
Other likely effects of the warming include more frequent occurrence of extreme weather events including heatwaves, droughts and heavy rainfall events, species extinctions due to shifting temperature regimes, and changes in agricultural yields. Warming and related changes will vary from region to region around the globe, though the nature of these regional changes is uncertain.
Proposed responses to global warming include mitigation to reduce emissions, adaptation to the effects of global warming, and geoengineering to remove greenhouse gases from the atmosphere or reflect incoming solar radiation back to space. The main international mitigation effort is the Kyoto Protocol, which seeks to stabilize greenhouse gas concentration to prevent a "dangerous anthropogenic interference".
As of May 2010, 192 states had ratified the protocol. The only members of the UNFCCC that were asked to sign the treaty but have not yet ratified it are the USA and Afghanistan.
In May 2011 a joint poll by Yale and George Mason Universities found that nearly half the people in the USA (47%) attribute global warming to human activities, compared to 36% blaming it on natural causes.
Only 5% of the 35% who were "disengaged", "doubtful", or "dismissive" of global warming were aware that 97% of publishing US climate scientists agree global warming is happening and is primarily caused by humans.
Researchers at the University of Michigan have found that the public's belief as to the causes of global warming depends on the wording choice used in the polls.
In the United States, according to the Public Policy Institute of California's (PPIC) eleventh annual survey on environmental policy issues, 75% said they believe global warming is a very serious or somewhat serious threat to the economy and quality of life in California.
Most scientists accept that humans are contributing to observed climate change. National science academies have called on world leaders for policies to cut global emissions. However, some scientists and non-scientists question aspects of climate-change science.
Organizations such as the libertarian Competitive Enterprise Institute, conservative commentators, and some companies such as ExxonMobil have challenged IPCC climate change scenarios, funded scientists who disagree with the scientific consensus, and provided their own projections of the economic cost of stricter controls.
In the finance industry, Deutsche Bank has set up an institutional climate change investment division (DBCCA), which has commissioned and published research on the issues and debate surrounding global warming.
Environmental organizations and public figures have emphasized changes in the current climate and the risks they entail, while promoting adaptation to changes in infrastructural needs and emissions reductions. Some fossil fuel companies have scaled back their efforts in recent years, or called for policies to reduce global warming.