Understanding climate change
Infra red emissions from warm bodies was first identified by Herscel in the 1850's. By the 1880, infra spectra had been measured.
Famously in 1902, Svante Arrhenius published a paper identifying the hazards of fossil fuel use, was picked up by the popular media. His critical observation was that carbon dioxide absorbs the infra red black body emissions from a 20C earth.
In 1988, James Hansen, then the director of the NASA Goddard Institute for Space Studies, stated to the U.S. Senate Energy committee “The greenhouse effect has been detected, and it is changing our climate now.”
The Vostoc ice cores taken from Antarctica, show the carbon dioxide in the air tracking temperature through the ice ages, the second graph shows the recent rapid increase in carbon dioxide way above previous concentrations since 1900.
By 2022, the impacts of climate change were affecting every corner of the earth through extreme weather and changes in the distribution of water. For example, major rivers are drying out, glaciers disappearing, along with massive floods.
The measured greenhouse effect shown in the graph below is around 1C per 100 ppm in CO2, in spectacular agreement with Arrhenius's original estimate of 1.3C
The current projections suggest that by 2100, there could be a 5C increase in temperature, and a 5 ft rise in sea level.
The effect of carbon dioxide on temperature takes around 500 years to reach equilibrium, with an additional 1-1.5C over the "immediate" impact.
The effect on the equilibrium sea level can be estimated based on what happened 100M years ago in the time of the dinosaurs. Carbon dioxide was 700ppm above current levels, temperatures were 10C higher, there were no ice caps and sea levels were a stunning 100m (330 ft) higher than today.
NASA climate database
If all the ice covering Antarctica, Greenland, (Antarctica would make about 60 meters of sea-level rise, Greenland about 7.4 meters), and in mountain ice caps around the globe were to melt, sea level would rise about 70 meters (230 feet) and cover all seaside cities.
Antarctic ice sheet weighs 24,380,000 gigatons, that is being lost at 40 ± 9 Gt/y from 1979 to 1990, 50 ± 14 Gt/y from 1989 to 2000, 166 ±18 Gt/y from 1999 to 2009 and finally 252 ±26 Gt/y from 2009 to 2017 for a roughly 1C rise.
For a 10C rise, a simple linear extrapolation suggests thousands of years to get to equilibrium ice levels for a given temperature.
In the short term it is estimated that by 2100 the rise could be 2m, probably 20x higher when ice melt equilibrates after 500+ years. These sea levels will force relocation of most sea edge cities in the world. The time scales emphasize that the changes we have seen already are nothing compared to what will happen as we reach equilibrium, and also how long it will take for the changes that we must make will have an impact.
Disruption of the earth currents are probably one of the most significant tipping point. The Atlantic Meridional Overturning Circulation (AMOC) carries warm water north from the Southern Hemisphere, where it releases heat and freezes. The freezing process concentrates salt in the non-frozen portion of the ocean water; this extra-saline water sinks, travels back south and picks up heat again, restarting the conveyor belt. (The Gulf Stream is part of this belt.) This release of heat helps keep Europe, and to some extent North America, balmier than it otherwise would be. But sediment records over the past 100,000 years suggest that, at times, the AMOC has shut down abruptly, leading to major climate shifts over mere decades. If the AMOC were to collapse in the near future, the consequences would be dire. Without the AMOC, the Northern Hemisphere would get colder, and the southern hemisphere would get warmer, though by a lesser degree . The effects vary by region, but Europe would be hard hit, van Westen said, cooling between 9 and 18 degrees Fahrenheit (5 to 10 degrees Celsius) within a century. That's a huge swing, even compared with the current level of climate change, which is already having impacts.
Without global warming, the earth is at a high temperature, low ice point in the last 400K years of ice age cycles. Loosing the polar ice will take us back to conditions that have not existed for 60M years. If/when the AMOC shuts off, Europe will initially cool and annual weather cycles will be disrupted. Then the global heating will take over and continue to melt.
AMOC strength has decreased by a few Sverdrups (1 Sv = 1E6 m3 s−1) from 2004 to 2012, from around 17 Sv. Longer timescale variability of the AMOC strength, estimated by using sea surface temperature (SST) time series based on “fingerprint” patterns (4), indicates that the AMOC weakened by 3 ± 1 Sv since about 1950. From proxy records, it has been suggested that the AMOC is currently in its weakest state in over a millennium (5).
Modelling suggests that collapse occurs at around 10 Sv, a drop of 40%. Patchy historical data suggests AMO dropping at 15% in 50 years, suggesting another 100 years before disaster.