As the sun's rays reach the Earth's surface
some are absorbed and re-emitted as heat
greenhouse gases such as water vapor and carbon dioxide
absorb and re-radiate some of this heat
increased amounts of greenhouse gases in the atmosphere mean more
heat is trapped
warming the Earth
human activities
especially the burning of fossil fuels have increased
concentrations of atmospheric carbon dioxide by 40%
mainly since 1900
global average surface temperature has increased by 0.8 degrees
Celsius over that time.
Other changes to the climate in recent decades,
can be seen in the warming of the oceans.
A rise in sea level
decreasing snow and ice cover in the northern hemisphere
and a decline in sea ice in the Arctic.
If emissions continue unchecked then further warming of 2.6 to
4.8°
Celsius would be expected by the end of the century.
Even at the low end.
This would have serious implications for human societies
and the natural world.
For more information about climate change from leading science academies,
please visit
royalsociety.org/climatechange
or nas-sites.org/americasclimatechoices