Climate Letter #1103

New details are available showing how Earth’s air temperatures increased between the depth of the last Ice Age and the warm period (Holocene) of the last 8000 years.  This post reviews a new study, one that I find a bit confusing, except that it includes an outstanding graphic of the globe which displays the best available information about how temperatures changed over about 12,000 years in all the different parts of the globe.  That chart is full of information and worthy of some extra comment.  It has long been known that during this period the polar regions warmed up about two or three times as much as the more temperate regions, but not based on the kind of detailed evidence now available, so scroll down to the chart and spend a few minutes getting familiar with it, following which I’ll have some comments.
Comments:
+In the temperate zone, from 30N to 30S, the air above the oceans warmed up by an average of just two or three degrees, and over land a bit more than that.
+Above 30N, to the north, everything warmed up by around ten degrees with the exception of the locations where the great ice sheets that once formed had melted down.  Those locations covered much of northern North America and northern Europe.  They are shown to have warmed up by 25-30 degrees.
+Greenland is interesting because it also had also formed an ice sheet, but it never did melt down, and Greenland has warmed up only by the same amount as everything else in the northern zone, including Siberia, which did not allow formation of an ice sheet for lack of enough moisture.  Greenland today averages about 20C colder than all other surfaces at that latitude, and that is because of its high altitude due to the thickness of all that ice that never melted down.  (When it does melt down, before too long, look for at least a 20 degree drop in its surface temperature.)
+In the Southern Hemisphere you need to look below 50S to find temperature increases in the ten degree range.  That includes the Antarctic continent, which, like Greenland, never did lose its two-mile overlay of ice and remained bitterly cold for that reason, also subject to change, eventually.
+I think the north will continue to warm up more rapidly than the south simply because there is relatively so much more land in the north, and land surfaces are known to regularly warm up a little more than oceans.  However, by exception, the south has a greater amount of the kind of ice-covered land that will some day lose all or much of its associated 20C differential due to elevation alone.  (There are also some built-in seesaw effects from shifting orbital cycles that one needs to consider.)
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Carbon footprint projections from the US Energy Department.  The new forecast, which is based on current trends and policies, sees only a small decline in emissions through 2050, with the growth in renewables failing to overcome the continued growth of natural gas consumption.  The US alone would thus use up most of the world’s remaining carbon budget of 200 billion tons of CO2.  While the assumptions are technically correct many forecasters see potential for a much faster transition to renewables in spite of what the Trump administration currently espouses.
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Things do not look too good for New Orleans.  The Atlantic magazine has a full-length feature story about various approaches that have been taken to engineer the city, roughly half of which is now below sea level.
Carl
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