The latest Special IPCC (U.N. Intergovernmental Panel on Climate Change) Report, authored by 91 scientists from 40 nations, says we’ve already warmed the planet by ~1.0 degs C and, if business remains as usual, we have only 12 years left before we’ve locked in 1.5 degs C of global warming, since the 20th century began.
However, Michael Mann and other prominent climate scientists say, as with previous IPCC reports, that this one is again watered-down and overly optimistic. They place the blame on the IPCC’s requirement for near-unanimity among, not just the authors, but also their reviewers (which may include bureaucrats and politicians), prior to formal publication. The often more dire, most recent, literature results also tend to be discounted for the same reason.
Though I suspect that the above criticism is quite valid, it alone does not provide a quantitative basis for assessment of the latest IPCC findings.
Here, I’ll address this concern by presenting three different quantitative estimates, all suggesting that the IPCC report presents, not a best case scenario, but an impossibly optimistic one.
Assuming “business as usual”, the approaches outlined below yield a tight cluster of estimates of 14.3, 13.5, and 12.7 years remaining to lock in, not just 1.5, but rather 2.0 degs C of warming since global temperature record keeping began in 1880. Thus, even the high end estimate of 14.3 years suggests that the IPCC’s forecast for the 12 year mark is overly optimistic by ~0.46 degs C.
Despite all professed concerns and counter-claims, the global CO2 emissions rate is still creeping upward. So, as yet, there’s nothing to suggest anything other than “business as usual” in our immediate future.
Meanwhile, those averse to high school math or prone to typing tl;dr (too long; didn’t read) can skip to the heading marked Items of Note.
Otherwise, I’ll be using (~) as shorthand for ‘roughly’; degs for ‘degrees’; C for ‘temperature in centigrade’; x for ‘multiplied by’; W/m^2 for ‘watts per meter squared’; ln for ‘natural log of’; ppmv for ‘parts per million by volume’; and EXP for ‘taken to the exponent of’.
According to the UC Berkeley BEST global temperature time series, we’ve already warmed ~1.1 degs C since 1880.
and for the past 25 years, the warming rate has been ~0.21 degs/C per decade.
We also have another ~0.6 degs C of global warming locked in, mainly because the oceans have an enormous amount of thermal mass that will take another ~40 years to fully equilibrate to the rise in atmospheric CO2 and other greenhouse gas concentrations.
Looking forward, this suggests a remaining margin of about 2.0 — 1.1 — 0.6 = ~0.3 degs C. Thus, we have a remaining grace period of
0.3 degs C/(0.21 degs C/decade) x 10 yrs/decade = ~14.3 years at “business as usual”,
immediately after which, we must drop the global CO2 emissions rate, or really its total greenhouse gas equivalent, to zero. Otherwise, we’ve locked ourselves into an inevitable 2.0 degs C of warming.
Indeed, 14.3 years for 2.0 degs C of warming and 0.21 degs C of warming per decade, suggests we’ll reach 2.0 degs C — (14.3 — 12.0 years) x 0.021 degs C/year =
1.96 degs C of warming within 12 years, not 1.5 degs C, as the Special IPCC Report suggests.
Caveats: 1) Note that shifting the base year from 1880 to 1900 to match the IPCC Report hardly makes any difference because the warming rate was negligible, ~0.04 degs C, between 1880 and 1900 (see graph above).
2) For several reasons I’ve used the data from the UC Berkeley BEST study. a) It was instigated by UC Berkeley physicist and former climate change skeptic, Richard Muller. b) Some seed money ($150k) came from the Charles G. Koch Foundation. c) It’s a careful analysis, synthesis and correction of data mainly gathered by the four government labs: NASA Goddard, NOAA, the UK Hadley Meteorological Office, and the Japan Meteorological Agency that still track global temperature data, since Australia’s CSIRO dropped out some years ago. d) Yet, the work is independent of government labs. That is, BEST is the study climate change deniers said they wanted and would abide by — until, to their horror, Muller testified under oath to the Congressional House Science and Technology Committee that:
“We see a global warming trend that is very similar to that previously reported by the other groups.” “Global warming is real.”
3) I’ve used the past 25 years to extrapolate a trend line because that’s about the shortest duration within which the +/- effects of outlier years can be subsumed, in order to establish a credible slope going forward.
Inverting the climate sensitivity equation also yields an estimate of how much time we have left.
The equilibrium climate sensitivity equation, in its most commonly displayed form, suggests that
delta T (temperature rise) = ~0.81 x degs C/(W/m^2) x 5.35 W/m^2 x ln (CO2 sought/CO2 original)
If so, a doubling of CO2 from its original, pre-industrial level of ~280 ppmv to 560 ppmv yields
0.81 x degs C/(W/m^2) x 5.35 W/m^2 x ln (2) = ~3.0 degs C of temperature rise.
But since we know that the temperature rise of interest to us is 2.0 degs C, we can invert the sensitivity equation to get the sought for CO2 level of interest:
CO2 = 280 ppmv x EXP( 2.0/(0.81x 5.35) ) = 444 ppmv
So, given we're now at ~409 ppmv and have been adding to that at ~2.6 ppmv per year for the past several years,
This yields (444 - 409 ppmv)/2.6 ppmv/year = ~13.5 years
to drop the global CO2 emissions rate to zero. 13.5 years is less than the 14.3 years found above, and obviously neither timetable is likely to be met, or even approached.
Caveat: There have been many estimates of the equilibrium climate sensitivity in the peer-reviewed research literature. And they have varied widely from ~1.5 to 4.5 degs C per CO2 doubling. Thus, a few years ago, a set of lower estimates for climate sensitivity were suggested, clustering around 2.0 degs C. These estimates coincide with data from the first decade of the 21st century that showed a possible warming hiatus or lull. The lull turned out to be no more than a warming slowdown, not a stoppage, reversed by more recent warming. This suggests that the “lull”, like earlier instances, was probably due to a natural back and forth sloshing of excess heat within the land/ocean/atmosphere climate system.
Indeed, the 3.0 degs C per CO2 doubling used above lies smack in the middle of two more recent estimates published this year.
Like annual deficit vs. total national debt, we know that, more than the emissions rate, the controlling factor is the total amount of CO2 released. That is,
a) the significance of the TOTAL tonnage of fossil-based CO2 (via oil, gas, and coal combined) released into the atmosphere, is based on two 2009 papers from the journal, Nature, one of the two most respected journals in science, Science being the other.
Note that the first paper was based on ensemble simulations from climate models, while the second was based on extrapolated/interpolated data observations.
Paper #1 says that adding more than 3.7 trillion tons of CO2 (half of which has already been released) to our atmosphere will exceed the +2 degs C warming level (beyond the pre-industrial era), albeit with rather large 95% confidence limits (1.3 to 3.9 degs C).
Paper #2 agrees, but also considers other contributing greenhouse gases: water vapor, methane, nitrous oxide, ozone, etc., which drop the solely carbon-based limit for total CO2 emissions to about 2.75 trillion tons.
If so, this means from Paper #2 that our atmosphere can withstand only ~2.75 trillion tons more in CO2 emissions, of which ~1.85 trillion tons had been emitted by 2006 (the latest data included in the 2009 papers). So, there’ve been ~36 billion tons per year of additional emissions during the past 12 subsequent years.
That’s 12 x 36 = 0.432 trillion tons. Thus, we have now emitted 1.85 + 0.432 = 2.28 trillion tons of CO2, leaving a “safety” margin of 2.75 — 2.28 trillion tons = 0.470 trillion or 470 billion tons of CO2 before we hit the dreaded 2 degs C warming limit.
With CO2 emissions currently at ~36.9 billion tons per year (as of 2017), that leaves us
470 billion tons/36.9 billion tons per year = 12.7 years,
which is even worse than the 14.3 or 13.5 years obtained from Methods 1 and 2 above. Thus, it remains rather likely that we’ll not only breach the dreaded 2.0 degs C limit, but also 2.5 and perhaps even 3.0 degs C.
Items of note:
a) Since the two papers driving Method 3 were published, real holes in their analysis or conclusions have yet to be found. And results from the IPCC modeling suite and others coincide with the basic findings, along with various observational data reviews.
b) The current man-made CO2 emissions rate of about ~4.5 ppmv (36 gigatons) per year is roughly double the actual yearly CO2 increase because the Earth's oceans and biosphere are now absorbing about ~60% of what’s emitted. However, whether the recent rise in airborne fraction will maintain itself remains debatable and is likely temporary.
c) Since the annual inventory of man-made CO2 (and other greenhouse gas) emissions is always much larger than the average annual CO2 increase, this also suggests, over the past century, that global warming has been all or nearly all man-made, particularly since all other plausible causes (solar brightening, volcanic eruptions, cosmic rays, planetary alignments, Earth orbital eccentricities, natural climatic variability, etc.) have been ruled out. Compare that with the IPCC’s weaker claim that climate scientists now have 95% confidence that global warming is largely man-made.
d) Burned oil constitutes ~43% of total CO2 emissions, which suggests, with “business as usual” that we can also only burn another ~ 0.43 x 37 billion tons x 14.3 years = ~227 billion tons of oil, which is only 13.4% of the ~1,700 billion tons of proven oil reserves.
This says, assuming “business as usual”, that the world's existing proven AND unproven oil reserves are really almost worthless. Since “proven reserves” constitute much of the book value for oil corporations, this will eventually impact their share prices.
Given the Arctic warming rate has been more than double the global average, the Nordic countries are bracing for up to 6 degs C of additional warming, for them a whole new and utterly chaotic world. Thus, Norwegians, for example, though rich in offshore oil, are scrambling to buy electric cars.
Nonetheless, the above seems consistent with what many climate scientists are muttering, or in the case of Dr. Michael Mann and a few others, loudly claiming.
If so, we can hope for:
a) no more of "business as usual". Of course, lending our reins to foreign autocrats and domestic wannabees detracts greatly from any mitigation efforts. For example, other than hydro, Putin’s Russia has essentially no credible, renewable energy program.
b) that the true climate sensitivity is somehow at the low end of estimates. A low end climate sensitivity would stretch considerably the number of years remaining before 2.0 degs C of warming is locked in.
c) that the cumulative CO2 tonnage limits are in reality too low, which is essentially the same as hoping for b). However, hopes based on b) or c) appear to be undercut by the result from Method 1, as it’s the most data-based and direct of the estimation methods.
d) that, pick your poison, we have some truly devastating (stratosphere breaching, sunlight dimming) volcanic eruptions pretty soon, AND
e) the airborne fraction (nature's ability to keep absorbing more than half of the released CO2) to continue. However, for 2016 we added 3.3 ppmv to global CO2 levels, which was well above the previous average of 2.6 ppmv.
If none of these hopes materialize, the above findings do not bode well.