Climate change includes both global warming driven by human emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.
The politics of climate change results from different perspectives on how to respond to the threat of global warming. Global warming is driven largely by the emissions of greenhouse gases due to human economic activity, especially the burning of fossil fuels. Ever since the industrial revolution, energy from fossil fuels has underpinned a large proportion of economic activity. So there has been much resistance to efforts to curtail their use. Nevertheless, efforts to mitigate climate change have been prominent on the international political agenda since the 1990s, and are also increasingly addressed at national and local level. In the 21st century, climate change adaptation is also receiving political attention.
Climate change is a complex global problem. Greenhouse gas (GHG) emissions contribute to global warming across the world, regardless of where the emissions occur. Yet the impact of global warming varies widely depending on how vulnerable a location or economy is to its effects. While global warming is on the whole having negative impact, with some areas already having suffered severe consequences, some only predicted to suffer more severe impacts in the future, other locations have benefited from the effects. Ability to benefit from both fossil fuels and renewable energy sources vary substantially from nation to nation. These and other differences resulted in early international conferences on climate change producing little beyond general statements of intent to address the problem, and non-binding commitments from the developed countries to reduce emissions. In some nations and local jurisdictions, climate friendly policies have been adopted that go well beyond what was committed to at international level. Yet local reductions in GHG emission that such policies achieve will not slow global warming unless the overall volume of GHG emission declines across the planet.
By the 2020s, the feasibility of replacing energy from fossil fuel with nuclear and especially renewable energy has much increased, with some countries now generating most of their electrical energy from renewables. Awareness of the climate change threat has risen, with many surveys showing a growing proportion of voters support tackling climate change as a high priority. Outright climate change denial had by 2019 became a much less influential force than in previous years. So, in several respects the prospects for reducing emissions have improved. Nevertheless, objectors to climate friendly policies remain, and the need to rapidly reduce emissions has became more urgent than ever. (Full article...)
Mean temperature anomalies during the period 1965 to 1975 with respect to the average temperatures from 1937 to 1946. This dataset was not available at the time.
Concentration of atmospheric CO 2 over the last 40,000 years, from the Last Glacial Maximum to the present day. The current rate of increase is much higher than at any point during the last deglaciation.
False-color image of smoke and ozone pollution from Indonesian fires, 1997
Carbon Dioxide observations from 2005 to 2014 showing the seasonal variations and the difference between northern and southern hemispheres
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
Global fossil carbon emissions 1800–2014
This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans in billions of metric tons of carbon per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon.
Probability density function (PDF) of fraction of surface temperature trends since 1950 attributable to human activity, based on IPCC AR5 10.5
Observed temperature from NASA vs the 1850–1900 average used by the IPCC as a pre-industrial baseline. The primary driver for increased global temperatures in the industrial era is human activity, with natural forces adding variability.
Frequency of occurrence (vertical axis) of local June–July–August temperature anomalies (relative to 1951–1980 mean) for Northern Hemisphere land in units of local standard deviation (horizontal axis). According to Hansen et al. (2012), the distribution of anomalies has shifted to the right as a consequence of global warming, meaning that unusually hot summers have become more common. This is analogous to the rolling of a dice: cool summers now cover only half of one side of a six-sided die, white covers one side, red covers four sides, and an extremely hot (red-brown) anomaly covers half of one side.
Solar irradiance (yellow) plotted together with temperature (red) over 1880 to 2018.
CO 2 sources and sinks since 1880. While there is little debate that excess carbon dioxide in the industrial era has mostly come from burning fossil fuels, the future strength of land and ocean carbon sinks is an area of study.
Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Carbon dioxide is not as strong a greenhouse gas as water vapor, but it absorbs energy in longer wavelengths (12–15 micrometers) that water vapor does not, partially closing the "window" through which heat radiated by the surface would normally escape to space. (Illustration NASA, Robert Rohde)
The Keeling Curve shows the long-term increase of atmospheric carbon dioxide (CO 2) concentrations from 1958–2018. Monthly CO 2 measurements display seasonal oscillations in an upward trend. Each year's maximum occurs during the Northern Hemisphere's late spring.
Modeled simulation of the effect of various factors (including GHGs, Solar irradiance) singly and in combination, showing in particular that solar activity produces a small and nearly uniform warming, unlike what is observed.
T. C. Chamberlin
Correspondence between temperature and atmospheric CO 2 during the last 800,000 years
Quantitative analysis: Energy flows between space, the atmosphere, and Earth's surface, with greenhouse gases in the atmosphere capturing a substantial portion of the heat reflected from the earth's surface.
James Hansen during his 1988 testimony to Congress, which alerted the public to the dangers of global warming
Energy flows between space, the atmosphere, and Earth's surface. Current greenhouse gas levels are causing a radiative imbalance of about 0.9 W/m2.
Global average temperatures show that the Medieval Warm Period was not a planet-wide phenomenon, and that the Little Ice Age was not a distinct planet-wide time period but rather the end of a long temperature decline that preceded recent global warming.
Radiative forcing drivers of climate change in year 2011, relative to pre-industrial (1750).
Biosphere CO 2 flux in the northern hemisphere summer (NOAA Carbon Tracker)
In 1896 Svante Arrhenius calculated the effect of a doubling atmospheric carbon dioxide to be an increase in surface temperatures of 5–6 degrees Celsius.
Air-sea exchange of CO 2
Top panel: Observed global average temperature change (1870— ). Bottom panel: Data from the Fourth National Climate Assessment is merged for display on the same scale to emphasize relative strengths of forces affecting temperature change. Human-caused forces have increasingly dominated.
Graph of CO2 (green), reconstructed temperature (blue) and dust (red) from the Vostok ice core for the past 420,000 years