Climate change includes both global warming driven by human-induced 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.
Climate tipping points are of particular interest in reference to concerns about global warming in the modern era. Possible tipping point behaviour has been identified for the global mean surface temperature by studying self-reinforcing feedbacks and the past behavior of Earth's climate system. Self-reinforcing feedbacks in the carbon cycle and planetary reflectivity could trigger a cascading set of tipping points that lead the world into a hothouse climate state.
Large-scale components of the Earth system that may pass a tipping point have been referred to as tipping elements. Tipping elements are found in the Greenland and Antarctic ice sheets, possibly causing tens of meters of sea level rise. These tipping points are not always abrupt. For example, at some level of temperature rise the melt of a large part of the Greenland ice sheet and/or West Antarctic Ice Sheet will become inevitable; but the ice sheet itself may persist for many centuries. Some tipping elements, like the collapse of ecosystems, are irreversible. (Full article...)
Correspondence between temperature and atmospheric CO 2 during the last 800,000 years
Carbon Dioxide observations from 2005 to 2014 showing the seasonal variations and the difference between northern and southern hemispheres
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.
Solar irradiance (yellow) plotted together with temperature (red) over 1880 to 2018.
A pictogram of the greenhouse effect
Erratics, boulders deposited by glaciers far from any existing glaciers, led geologists to the conclusion that climate had changed in the past.
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.
False-color image of smoke and ozone pollution from Indonesian fires, 1997
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.
James Hansen during his 1988 testimony to Congress, which alerted the public to the dangers of global warming
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.
Biosphere CO 2 flux in the northern hemisphere summer (NOAA Carbon Tracker)
Graph of CO2 (green), reconstructed temperature (blue) and dust (red) from the Vostok ice core for the past 420,000 years
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.
Annual CO 2 flows from anthropogenic sources (left) into Earth's atmosphere, land, and ocean sinks (right) since year 1960. Units in equivalent gigatonnes carbon per year.
Biosphere CO 2 flux in the northern hemisphere winter (NOAA Carbon Tracker)
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.
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.
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.
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)
Global fossil carbon emissions 1800–2014
Radiative forcing drivers of climate change in year 2011, relative to pre-industrial (1750).
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
Greenhouse gases allow sunlight to pass through the atmosphere, but then absorb and reflect the infrared radiation (heat) the planet emits
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.
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.
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.
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.
Probability density function (PDF) of fraction of surface temperature trends since 1950 attributable to human activity, based on IPCC AR5 10.5
The effective rate of change in glacier thickness, also known as the glaciological mass balance, is a measure of the average change in a glacier's thickness after correcting for changes in density associated with the compaction of snow and conversion to ice. The map shows the average annual rate of thinning since 1970 for the 173 glaciers that have been measured at least 5 times between 1970 and 2004. Larger changes are plotted as larger circles and towards the back.
All survey regions except Scandinavia show a net thinning. This widespread glacier retreat is generally regarded as a sign of global warming.
During this period, 83% of surveyed glaciers showed thinning with an average loss across all glaciers of 0.31 m/yr. The most rapidly growing glacier in the sample is Engabreen glacier in Norway with a thickening of 0.64 m/yr. The most rapidly shrinking was Ivory glacier in New Zealand which was thinning at 2.4 m/yr. Ivory glacier had totally disintegrated by circa 1988.