Rising temperatures and sea levels

If you are like me, you probably saw a headline like this one the other day: U.S. Report Says Humans Cause Climate Change, Contradicting Top Trump Officials

And if you are like me, you may not have read the story. How could I stand absorbing yet another hopeless attempt by scientists to get through to the fossil-fuel deluded numbskulls who control climate policy? Besides, understanding the science is hard; I trust the scientists and usually stick to thinking about the politics, more in my line of expertise.

But while searching weather reports, I came across a succinct description of the National Climate Assessment by Bob Henson: Humans Likely Responsible For Virtually All Global Warming Since 1950s. It seems worthwhile to share some of the main points.

On temperatures:

• Warmest in more than a thousand years. A major paleoclimate study has shown that for each of the world’s seven major continental regions, the average temperature for 1971-2000 was the highest in more than 1300 years. There is significant uncertainty around these estimates, but a separate study found that temperate North America as a whole (including most of the contiguous U.S.) is having its warmest 30-year periods in at least 1500 years.

• It’s going to get a lot warmer in the coming decades. Temperatures across the contiguous U.S. have risen about 1.8°F (1.0°C) over the period 1901-2016. “Surface and satellite data are consistent in their depiction of rapid warming since 1979,” the report notes. By the period 2070-2100 (when today’s infants will be elders), U.S. temperatures may be 2.8 to 7.3°F warmer than the 1976-2005 average if greenhouse-gas emissions are reined in strongly—or 5.8 to 11.9°F warmer if emissions continue to grow at the pace of recent decades.

On sea levels:

• U.S. coasts will experience more than the global average sea level rise from Antarctica Ice Sheet melt, and less than the global average from Greenland Ice Sheet melt. These results are both produced by what’s called static-equilibrium effects—basically, how the planet’s gravity and rotation are affected by moving huge volumes of water from polar ice sheets into the global oceans.

• The Northeast U.S. coast is expected to see additional sea level rise because of a gradually weakening Atlantic meridional overturning circulation, which helps power the Gulf Stream. Much as the polar jet stream separates air masses of different densities, the Gulf Stream separates warmer, less-dense water and higher sea levels on its southwest side from denser, cooler water and a lower sea level on its northwest side, toward the Northeast U.S. coast. Any long-term weakening of the Gulf Stream would be associated with a reduced sea-level gradient, and that would mean a drop in sea level toward the southeast and a rise toward the northwest (on top of any global-scale changes, of course).

• Regional sea level rise is being exacerbated by withdrawals of groundwater off the Atlantic coast, and withdrawals of both fossil fuels and groundwater off the Gulf Coast. If these continue, so will the regional effects.

And that's just a sampling. Read it all. Our only hope of interrupting greed and stupidity depends on daring to face the violence our species is doing to our only home.