Scientists project intensifying impacts from future climate change

Climate change has already been observed in many Earth systems; these changes are documented in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, published in 2007.[[IPCC, 2007: Climate Change 2007: Synthesis Report. (PDF) Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. eds.)] IPCC, Geneva, Switzerland, 104 pp.]]. Like earlier versions, this report is a synthesis of hundreds of individual peer-reviewed scientific papers on the causes and effects of climate change.

The most recent IPCC report, like the three major IPCC reports that preceded it, also projects future changes in the climate, based on varying assumptions about future emissions of greenhouse gases and other factors — and also on the best current understanding of the physical processes that dominate climate.

Those projections, along with newer projections based on subsequent research, show that most if not all of the trends that have been observed in current climate are likely to intensify through the coming century as atmospheric concentrations of greenhouse gases increase.

In particular, temperatures will rise faster in the coming decades than they have so far; sea level and ocean acidity will rise more quickly; the incidence of certain insect infestations will increase, as will wildfires, droughts, extreme weather events. The extinction of species is likely to accelerate as ecosystems shift or disappear entirely. Mountain glaciers are likely to melt back or disappear, leading to increased pressure on water supplies even as population growth triggers increased demand for water. Shifts in weather patterns will likely cause disruptions in agriculture. The Arctic Ocean is likely to become ice-free for at least part of the summer.

This is only a partial list. Moreover, while IPCC reports are considered the gold standard in climate-change science, other reports are taken seriously as well; among them is a June, 2009 document from the US Global Change Research Program, which focuses on the projected regional impacts of climate change within the United States.[[The full report, or smaller, regional reports.]]