Scenarios studied by the Intergovernmental Panel on Climate Change (IPCC) predict that global warming will continue and get worse much faster than was expected even in their last report. Research by NOAA indicate that the effects of global warming are already irreversible. The IPCC reports attribute many specific natural phenomena to human causes. The expected long range effects of recent climate change may already be observed. Rising sea levels, glacier retreat, Arctic shrinkage, and altered patterns of agriculture are cited as direct consequences of human activities. Predictions for secondary and regional effects include extreme weather events, an expansion of tropical diseases, changes in the timing of seasonal patterns in ecosystems, and drastic economic impact. Concerns have led to political activism advocating proposals to mitigate, or adapt to it. Geoengineering is a further potential response, which could potentially reverse some effects that may otherwise be irreversible.
It is notable that many of the effects of global warming are non-linear in nature, with potential for dramatic positive feedback effects. This means that the climate may enter a critical state where small changes can trigger runaway or abrupt climate change. Geoengineering has been suggested as a means of interrupting or reversing these effects. A notable example of a 'runaway' effect is the release of methane from clathrates (known as the clathrate gun effect).
The 2007 Fourth Assessment Report by the IPCC includes a summary of the expected effects.