Global Warming Has Reached Nearly +1.5°C Already

Slide 5 from the "NOAA/NASA Annual Global Analysis for 2016" (pdf here; click to enlarge image). As you'll read below, global temperature in 1910 is a good proxy for "pre-Industrial global temperature." Thus, converting °F in the chart to °C, global warming has reached nearly +1.5°C already. More than +0.2°F (+0.1°C) or that rise came in just the last two years.

by Gaius Publius

I wrote recently about Trump, climate change and the upward march of global temperature: "Trump Takes Office Following the Three Hottest Years in Recorded History." Now I'd like to extend that idea in a couple of easy charts and one added thought.

The first chart is below. Let's start with a broad look at average global temperature during the Holocene, the period during which our species came out of the Stone Age, became civilized (i.e., lived in settlements; "civilization" has the same root as "city") and entered the modern era.

The Holocene starts around 12,000 years ago, at the end of the most recent ice age, as the last ice receded and the earth warmed to its current temperature range.

Global average temperature during the Holocene. Blue curve: Global temperature reconstruction from proxy data of Marcott et al, Science 2013. Recent instrumental measurements shown in red (global temperature from the instrumental HadCRU data). Graph: Klaus Bitterman. (Source; my annotation; click to enlarge)

In this chart, "zero" on the Y-axis is the average global temperature in the years 1961–1990. The zero point doesn't matter though; what matters is where the most recent low (the "pre-industrial global temperature") is. I've pointed it out in the chart.

("Pre-industrial temperature" refers to the average surface temperature of the earth prior to the start of the Industrial Revolution — the year 1781 when the James Watt steam engine was invented. But it's generally taken to be around 1800, before the climate effects of industrialized coal-burning became apparent. "Pre-Industrial temperature" is a commonly used start point for measuring global warming. A statement like "global warming of +2°C" means "a 2°C increase above pre-Industrial temperature.")

Note, as you look at the chart of the entire Holocene above, that the oldest civilizations, like the Sumerian, date to only 5,000 BCE or so, and proto-writing appears no earlier than about 3,000 BCE or later.Through more than half of this period, humans remained in the Stone Age.

Note also that the Holocene temperature range, from lowest temperature to highest, is no greater than about 0.7°C — less than one full degree of average temperature fluctuation for the entire period. Of course, regional variations have been much greater, but it's the globe as a whole we're concerned about. Thanks to the narrowness of this temperature range, there have always been many places on earth, not just a few, for humans to flourish. Had there been just a few, our population would be much smaller and "civilization" (humans in settlements) would have been much less wide spread.

Put differently, all of human civilization existed on a planet whose average temperature fluctuation was about two-thirds of a degree Celsius. The "pre-Industrial temperature" is also the modern low of that temperature range.

In the next chart, let's look at the end of the above time period, the final 1000 years, in greater detail.

(Source; click to enlarge)

The time frame covers from the year 1000 to about 2013 (2013 is the publication date; the last data sample may be from 2012). The blue line now shows the "PAGES2K" temperature reconstruction, but it gives similar results to the Marcott reconstruction (as discussed by climate scientist Stefan Rahmstorf here).

Note that the global temperature low at about 1900–1910 (the first deep dip in the instrumental readings, the red line) is a good proxy for the pre-industrial temperature low pointed out in the chart. We can take the temperature in that later period (1900 or so) to be nearly the same as the "pre-Industrial low."

Now look at the chart at the very top, from the recent "NOAA/NASA Annual Global Analysis for 2016" (pdf). Note that global average temperature from the low of 1910 to the 2016 high runs from –0.8°F to +1.8°F, a difference of 2.6°F — or 1.44°C — above the 1910 low. (It's a little less in other datasets — for example, see Slide 4 of the same report — but not by enough to matter.)

Two points:

• The Paris climate agreement had hoped to hold global warming to no more than +1.5°C above the pre-Industrial temperature. This is not going to happen. We're almost at that point now, and we'll breach that goal in just a few years.

• From the chart at the top, note that the two-year rise from 2014 to 2016 was, converted to Celsius, +0.1 degrees all on its own. Three more two-year periods like this and global temperatures will cross +2°C, the extremely generous IPCC "magic barrier" after which, in lay language, "we're mainly screwed."

This doesn't mean we should do nothing to adapt to the blow — it's always necessary and wise to adapt, even if the start of adaptation is very late. But the window to mitigate — to lessen the blow — is rapidly closing. Remember, once the social and political chaos reaches critical mass (once there's too much of it), global warming will run to its natural conclusion.

Elsewhere I've predicted the "natural conclusion," barring conscious intervention, to be global warming of +7°C before humans are forced to stop emitting so much CO2, either through greatly diminished numbers, or greatly diminished technology, or both.

Global Average Temperature and Donald Trump

Now the added thought. As of this minute, we humans aren't slowing or stopping our carbon emissions. We continue to add carbon emissions to the atmosphere at close to 10 GtC (gigatons of carbon) per year — or, if you measure the CO2 emitted instead of the carbon burned, by more than 3.67 GtCO2 per year. (GtC and GtCO2 are two ways of measuring the same thing. GtC measures the amount of carbon burned. GtCO2 measures the CO2 it becomes after being burned.)

With Trump in office, the rate will surely increase. First, he is determined to encourage exploitation and extraction of U.S. fossil fuels to the greatest extent possible. Any fuel extracted will be burned. Second, U.S. abandonment of "carbon restraint" will encourage the same behavior by other energy-poor countries like India. Third, world leadership, both moral and practical, in the fight against climate change will pass from the U.S. to either Europe, China, or both.

In which case, fourth, the U.S. will be come a pariah among nations, whether the rest of the world drowns itself or saves itself in the climate decade ahead.

Unless, of course, he pushes people too far and they "Easter Island" his regime instead.

There's always a choice, and we make it every day. Just sayin'.

[Update: Fixed a minor math error.]

GP