Physical impacts for global warming

Main article: Physical impacts of climate change

Seven of these indicators would be expected to increase in a warming world and observations show that they are, in fact, increasing. Three would be expected to decrease and they are, in fact, decreasing.[31] A broad range of evidence shows that the climate system has warmed.[33] Evidence of global warming is shown in the graphs opposite. Some of the graphs show a positive trend, e.g., increasing temperature over land and the ocean, and sea level rise. Other graphs show a negative trend, e.g., decreased snow cover in the Northern Hemisphere, and declining Arctic sea ice extent. Evidence of warming is also apparent in living (biological) systems.[34] Human activities have contributed to a number of the observed changes in climate.[35] This contribution has principally been through the burning of fossil fuels, which has led to an increase in the concentration of GHGs in the atmosphere.[36] Another human influence on the climate are sulfur dioxide emissions, which are a precursor to the formation of sulfate aerosols in the atmosphere.[37] Human-induced warming could lead to large-scale, irreversible, and/or abrupt changes in physical systems.[38][39] An example of this is the melting of ice sheets, which contributes to sea level rise.[40] The probability of warming having unforeseen consequences increases with the rate, magnitude, and duration of climate change.[41