Physical environment

The environmental effects of global warming are broad and far-reaching. They include effects on the oceans, ice, and weather and may occur gradually or rapidly.

Between 1993 and 2017, the global mean sea level rose on average by 3.1 ± 0.3 mm per year, with an acceleration detected as well.^[124] Over the 21st century, the IPCC projects that in a high emissions scenario the sea level could rise by 61–110 cm.^[125] The rate of ice loss from glaciers and ice sheets in the Antarctic is a key area of uncertainty since this source could account for 90% of the potential sea level rise.^[126] Increased ocean warmth is undermining and threatening to unplug Antarctic glacier outlets, potentially resulting in more rapid sea level rise.^[127] The retreat of non-polar glaciers also contributes to sea level rise.^[128]

Global warming has led to decades of shrinking and thinning of the Arctic sea ice, making it vulnerable to atmospheric anomalies.^[129] Projections of declines in Arctic sea ice vary.^[130] While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2.0 °C^[131] increasing the ice–albedo feedback.^[132] Higher atmospheric CO₂ concentrations have led to an increase in dissolved CO₂, which causes ocean acidification.^[133] Furthermore, oxygen levels decrease because oxygen is less soluble in warmer water, an effect known as ocean deoxygenation.^[134]

Many regions have probably already seen increases in warm spells and heat waves, and it is virtually certain that these changes will continue over the 21st century.^[135] Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency.^[136] Extremely wet or dry events within the monsoon period have increased in India and East Asia.^[137] Various mechanisms have been identified that might explain extreme weather in mid-latitudes from the rapidly warming Arctic, such as the jet stream becoming more erratic.^[138] The maximum rainfall and wind speed from hurricanes and typhoons are likely increasing.^[139]

Long-term effects of global warming: On the timescale of centuries to millennia, the magnitude of global warming will be determined primarily by anthropogenic CO₂ emissions.^[140] This is due to carbon dioxide's very long lifetime in the atmosphere.^[140] The emissions are estimated to have prolonged the current interglacial period by at least 100,000 years.^[141] Because the great mass of glaciers and ice caps depressed the Earth's crust, another long-term effect of ice melt and deglaciation is the gradual rising of landmasses, a process called post-glacial rebound. This could be facilitating seismic and volcanic activity in places like Iceland.^[142] Tsunamis could be generated by submarine landslides caused by warmer ocean water thawing ocean-floor permafrost or releasing gas hydrates.^[143] Sea level rise will continue over many centuries.^[144]

Abrupt climate change, tipping points in the climate system: Climate change could result in global, large-scale changes.^[145] Some large-scale changes could occur abruptly, i.e. over a short time period, and might also be irreversible. One potential source of abrupt climate change would be the rapid release of methane and carbon dioxide from permafrost, which would amplify global warming.^[146] Another example is the possibility for the Atlantic Meridional Overturning Circulation to slow or shut down (see also shutdown of thermohaline circulation).^[147] This could trigger cooling in the North Atlantic, Europe, and North America.^[148]