The best climate news

 I've mentioned this before.  

On February 17, CCNow held a joint press briefing with Scientific American on a little-known scientific development that carries paradigm-shifting implications for how people think and feel about the climate crisis and how governments and societies respond to it.

Most journalists have long echoed what we thought was the scientific consensus: Even if greenhouse gas emissions stop, global temperatures will keep rising for 30 to 40 more years, mainly because of carbon dioxide’s long lifetime in the atmosphere. But in fact the latest science doesn’t say that. The lag time for temperature rise would actually be as little as 3 to 5 years, as was noted in the latest IPCC report last August and explained in a Scientific American article last October.

The phrasing employed by the IPCC scientists is, unfortunately, not easy for non-scientists to decipher, but the following is a lay person’s guide. The key graph is the bottom of the two graphs in Figure 1.5, and the key sentence is the fourth sentence in the box of text to the right of that graph. That sentence reads: “Temperatures continue to increase slightly after the elimination of CO2 emissions (blue line) in response to constant non-CO2 forcing.” A more reader friendly way to phrase this would be—we’ve added emphasis and extra wording here with italics–“Temperatures continue to increase only slightly after the elimination of CO2 emissions (blue line)…” Here, “only slightly” refers to the 3 to 5 years of additional warming that Michael Mann cited, while “elimination” refers to the hypothetical case of humanity halting all greenhouse gas emissions overnight.

You can visualize this potential halt in temperature rise by looking at the solid blue line in the bottom of the two graphs, which proceeds in an almost perfectly straight line from left to right, depicting how temperatures would remain virtually flat out to the year 2100. Be careful to follow the solid blue line and not the dotted blue line or the dashed blue line, which depict radically different scenarios.

I thought the chart very useful.

Source: The Best Climate Science You’ve Never Heard Of

The top chart shows "forcing" in watts per square metre.  Forcing is the energy flux (how much energy accumulates, netting out the inflow (from the sun) and radiation from the earth.)  As forcing becomes more positive, global temperatures rise.  (Read the Wikipedia article for a more scientific definition and explanation.)  The temperatures on Earth rise and fall following radiative forcing, with a lag.    

The bottom chart shows the temperature, with the left axis the temperature change since 2020, and the right the temperature above pre-industrial averages.  The dashed blue line shows how temperatures will go on rising if the trend since 1980 (± 0.2 degrees C) continues.  The blue line (close to horizontal in the bottom chart, falling in the top) shows the temperature/forcing if we suddenly stopped emitting CO2, but kept on emitting methane (CH4)  and Nox (NO2).  The pink/purple line shows what would happen if we stopped emitting all greenhouse gases (mainly CO2, NO2 and CH4).  The green line shows the temperature (lower chart) and forcings (upper chart) if we stop emitting CO2 and also stop emitting aerosols.  Aerosols reflect incoming sunlight (including infra-red) back into space, so they reduce global warming.  The dotted line shows what happens with a 50-year phaseout of CO2 emissions, but all other forcings (CH4, NO2 and aerosols) constant.  A 50-year phaseout implies net-zero by 2070, not 2050.

The key points from this analysis are:

• If we stop emitting greenhouse gases, forcings stop rising within 3 to 5 years.  See how in the top chart, forcings jump sharply(green line) if we stop both CO2 and aerosols but not other GHGs, then declines steadily.   Temperatures jump (bottom chart) but then rise only slowly.
• If we stop all GHG emissions (CO2, NO2, CH4) but continue with aerosols, both forcings and temperatures peak immediately, and in fact temeratures start to fall, by about 0.4 degrees from 2020 levels.
• If we cut CO2 emissions to zero over the next 50 years, the rise in global temperatures since pre-industrial times is just a whisker over 1.5 degrees.

Some people will interpret this good news as meaning that we need take no action to cut emissions, that everything will be all right.  This is wrong. Look again at the dashed blue line.  If we take no action, temperatures will go on rising by 0.2 degrees a decade.   

The clear implication of this research is that the sooner we cut emissions, the sooner global temperatures will stop rising.  We won't have to wait decades for the global climate system to respond.  If we transition electricity generation to renewables and our vehicle fleet to electric engines, the world will be able to cut emissions by 50%.  We should do that as soon as possible.