Effects

The effects of global warming are the environmental and social changes caused (directly or indirectly) by human emissions of greenhouse gases. There is a broad scientific consensus that climate change is occurring, and that human activities are the primary driver.^[1] Many impacts of climate change have already been observed, including extreme weather events, glacier retreat,^[2] changes in the timing of seasonal events^[2] (e.g., earlier flowering of plants),^[3] changes in agricultural productivity,^[2] sea level rise, and declines in Arctic sea ice extent.^[4]

The physical effects of future climate change depends on the extent of prevention efforts (i.e., reducing greenhouse gas emissions). The social impact of climate changes will be further affected by our efforts to prepare for changes that do occur.^[5][6] Climate engineering is another policy option, although there are uncertainties regarding its effectiveness and little is known about potential side effects.^[7]

Near-term climate change policies could significantly affect long-term climate change impacts.^[5][8] Stringent mitigation policies might be able to limit global warming (in 2100) to around 2 °C or below, relative to pre-industrial levels.^[9] Without mitigation, increased energy demand and extensive use of fossil fuels^[10] might lead to global warming of around 4 °C.^[11][12] Higher magnitudes of global warming would be more difficult to adapt to,^[13] and would increase the risk of negative impacts.^[14]