Overview Studies - IPCC
How do we know humans are causing climate change?
Humans produce large amounts of greenhouse gas emissions, primarily through fossil fuel burning, agriculture,deforestation and decomposing waste.
-IPCC Sixth Assessment Report
Bars showing % of the 56 or more studies considered that found various % yield changes (color key at right). The black horizontal bars show the line between yields higher than now and lower ones. Farther into the future, more and more studies project lower yields, especially much lower yields. Assumptions about adaptation, CO2 fertilization and other matters varied from study to study.
Forecast Changes as Fraction of Global Mean Change
CMIP3 models are vintage ~2004, while CMIP5 models are vintage ~2011. Relative temperature changes on 97% of land exceed mean global temperature changes (red, dark red & purple), especially in the Arctic, while relative changes over 92% of the oceans (not the Arctic) are less than mean global temperature change (orange & light orange). Temperatures change more toward the poles.
These are relative to the global mean. For absolute projections of temperature change,see the maps from the 2014 Impacts summary, a bit above the 2013 Science Assessment.
That is, land surfaces warm faster than ocean surfaces.
Precipitation changes, however, are location-specific % changes relative to now. Increases will be strongest in the Arctic, while decreases will be greatest around the Mediterranean.
Permafrost loss could be as high as 88% by 2100 in the highest emission scenario.
CO2 removal processes cannot keep up with huge, swift CO2 injections. Removal goes much slower, %-wise.
2012: Extreme Weather Events & Climate: Summary of Policymakers - PDF, 20 pp. Some diagrams are larger on web.
2007: Summary for Policy Makers - PDF, 22 pp
Science Summary - PDF, 21 pp
Damages Summary - PDF, 23 pp
Mitigation Summary - PDF, 35 pp
Overall Summary - PDF, 23 pp
2001: Agriculture and Ecosystems - PDF, 108 pp
Water - PDF, 43 pp
Section Map: Overviews