Climate crisis: Why we’re on track for 7°C (12°F) warming or greater by 2100

This is the third part in our three-part series, Climate Crisis: The View from 10,000 Feet. The three parts are:

▪ The climate crisis in three easy charts
▪ A closer look at global temperature, both before and during the age of man
▪ Climate crisis: Why we’re on track for 7°C (12°F) warming or greater by 2100 (this piece)

These three essays together form the opening chapter of a book I’m working on. They present the long view and put the discussion in historical context. There are no more important questions than these, especially given the nearness of the deadlines:

What’s the history of climate on earth, from the flowering of life through today?
What’s the history of climate during man’s time on earth?
Where are we headed and when?

The first half of this essay recaps the answers to the first two questions above. To jump to the new material — Where are we headed and when? — click here.

There’s a lot of detail in this discussion, but only one bottom line — what happens when? We now know enough to answer that question rather closely. If we don’t “stop now” — meaning, hit the carbon brake hard and stop the carbon car — we risk going over a cliff whose edge could be as near as five to ten years away.

What we’ve learned so far

In our overview to this series, “The climate crisis in three easy charts,” we looked at the beginning, middle and end of the history of life on earth — “end” means “where we are now” — and the climate during these periods.

We saw that, starting 540 million years ago, when life exploded in abundance on this planet — first in the sea, later on land — there have only been three geologic eras, each divided from the other by major mass extinction events that marked the shift from one dominant kind of life (group of species) to another. Those eras are:

The Paleozoic Era  — the period of “old life,” or the pre-dinosaur era
The Mesozoic Era — the period of “middle life,” or the age of reptiles and dinosaurs
The Cenozoic Era (now) — the period of “new life,” or the age of mammals and man

The Paleozoic Era started with the explosion of life in the Cambrian, 540 million years ago (“mya”), and ended 250 million years ago with the “Great Dying,” the greatest mass extinction event in earth’s history.  All large species (some were very large), and almost all species of any type, went extinct. This opened a niche for reptiles and soon, dinosaurs, to grow and flourish.

The Mesozoic Era ended 65 million years ago, with a mass extinction that wiped out all of the non-avian (non-bird) dinosaurs and most large species of any type. This opened a niche for mammals to develop and thrive in the Cenozoic Era, which is where we are now.

Mass Extinctions since the Cambrian Period (540 million years ago)

Mass extinctions since the Cambrian Period (540 million years ago)

First bottom line — Eras of life on earth end with significant mass extinction events. As the chart above also shows, mass extinctions mark other geological boundaries as well.

In the second piece in our series, “A closer look at global temperature, both before and during the age of man“, we examined a chart of temperatures across this 540-million-year time period and saw a remarkable story.

That temperature data is represented in the chart below (click to enlarge). As you see in the left half of the chart, there are considerable spikes in global temperature, mainly to the upside, from the Cambrian through about 15 million years ago, with the highest spike reaching almost +8°C from pre-Industrial norms. (Everywhere on this chart, the zero line — “0 ΔT (°C)” — means “difference in temperature from the pre-Industrial norm,” which can be seen as a solid black line during the “Holocene,” on the extreme right end.)

Global temperatures from the Cambrian through today

Global temperatures from the Cambrian through the present

(Note: For temperatures from the “15 mya” mark to the present — that is, for the last three time periods, known as the PliocenePleistocene and Holocene — use the “Equivalent Vostok ΔT (°C)” scale for temperatures on this chart. I’ve circled it above and added a dotted horizontal line to show roughly where +2°C is.)

Starting at roughly 15 million years ago, however, things change and global temperature spikes never reach above +2°C or so from modern norms.  Fifteen million years is a drop in the bucket compared to the time spanned by the previous 525 million, but it’s the period we’re most interested in, since it includes the time in which man appears and develops.

Keep that +2°C or so in mind, since if we don’t stop carbon use very soon, global warming is certainly headed above that.

All major spikes after about 15 mya are to the downside, producing a long period of intermittent glaciers and ice ages. Modern ice ages start around 3 million years ago, near the end of the Pliocene, and end when the Pleistocene ends, about 12,000 years ago. (The boundary between the Pliocene and the Pleistocene has been moved back recently, to about the 2.5 million-year mark, but this doesn’t affect our analysis. The chart above reflects the previous boundary.)

Life in the Holocene (“today”)

This takes us to the present, called by geologists the Holocene Epoch. It’s the right-most division on the chart above. It’s also the age of agricultural and civilized life. (Interesting naming fact — the names of the last three epochs, Pliocene, Pleistocene and Holocene, come from Greek roots that mean “more new,” most new” and “entirely new.”)

“Agricultural life” refers to human life during what scientists call the “neolithic revolution” — the “wide-scale transition of many human cultures from a lifestyle of hunting and gathering to one of agriculture and settlement which supported an increasingly large population.” This begins around 12,000 years ago and spreads to encompass almost all cultures.

“Civilized life” refers to a way of life that generally includes a stable ceremonial center (a palace or temple), some form of writing, and something like a city, as opposed to just tribes and villages. Civilization in this sense started roughly 10,000 years ago and spread widely. “Civilized life” is the way most of us live today.

The “Holocene” and the “age of civilization” can therefore be considered identical. Here’s that same temperature chart again, but trimmed to focus on just the lower quadrant. Use the “Equivalent Vostok” scale (circled) for temperature readings.

Global temperatures, focusing on the ice ages and the age of civilized man

Average global temperatures, focusing on the ice ages and the age of civilization

Note the remarkable flatness of average global temperature during the Holocene. Note that temperatures never rise much above +2°C for the period pictured, and in the Holocene, they never rise above (or fall below) ½°C (0.5°C for the math majors) — until the very end when the Industrial Revolution begins.

That’s an amazing consistency in temperature. While regional temperatures have varied more widely, the earth as a whole has stayed within a very narrow range — ±½°C — through the entire period until very near the end. As I wrote in the second piece in this series:

The flattening of global temperature in the last 10,000 years … coincides exactly with civilized man, man emerging from hunter-gatherer status to build villages and farm land. It would be nice to keep the earth in that range, right?

Again, from the chart above, “Modern age of glaciers” is the period of hunter-gatherers; the Holocene, which immediately follows, is the time of “Agriculture & civilization.” The correspondences could not be more clear.

Given all of this, we asked in that piece the critical questions — What temperature will trigger another mass extinction? Which temperature will drastically upset this balance? The most widely accepted answer — though certainly not the only one — is offered by James Hansen, NASA global warming expert. Hansen has written that keeping global warming below 3°C is critical for our survival.

In his words (pdf; my emphasis):

If global warming approaches 3°C by the end of the century, it is estimated that 21-52% of the species on Earth will be committed to extinction.

Since scientists are naturally conservative, and since everything about global warming is happening faster than anyone expected, I’d take the higher percentage of extinctions seriously.

Think about a 50%–mass extinction event. What kind of world would we be living in, if global warming were killing half of all species on earth and drastically shrinking the human-livable world? How would it change the age of man? Would it end the Cenozoic Era? This piece explores those questions.

What we don’t want to lose — a brief review

Before we proceed further, let’s review what we’ve seen to this point:

▪ For a very long period, from the Cambrian until about 15 million years ago, global temperatures have swung widely, spiking up to +7°C or more, and down to –2°C, measured against modern (“age of man”) average temperature.

▪ More recently we entered a period of ice ages, in which global temperatures rarely exceeded 2°C above the modern norm. During this period, hominids evolved. Late in this period, man (homo sapiens) evolved.

▪ Then 12,000 years ago, we entered a time (the Holocene, “today”) in which average global temperatures stay within a very narrow range, ±½°C of the global average for the period. For the last 12,000 years, we’ve seen almost no global fluctuation.

During this period, man settles down, becomes a farmer and builds cities. Our lives today — civilized, settled, technological — are products of the Holocene and are entirely encompassed by it.

It’s quite a story, isn’t it? Here’s a closer look at temperatures during the Holocene, illustrating the third bullet above.

Average global temperatures during the Holocene, the last 12,000 years (updated through 2004)

Average global temperatures during the Holocene, the last 12,000 years

The solid black line shows global averages. The colored lines show eight records of local temperature variability used to produce this average. Life during the age of civilization, all within about ±½°C.

The “Holocene normal temperature” and the “pre-Industrial normal temperature”

A word about definitions before we go on. As noted, the Holocene is the epoch we’re in today. It starts about 12,000 years ago when earth emerged from its last ice age. The “Holocene normal temperature” — the global average of regional temperatures — is essentially zero on all graphs of the type we’ve been showing.

This norm holds more or less intact through the year 1800, at which point the Industrial Revolution, which started around 1760, began to have a warming effect. The Industrial Revolution was driven in no small part by the coal-powered steam engine invented by James Watt and patented in 1781. The Industrial Revolution is also the “first carbon era” in Michael Klare’s nomenclature.

Thus the “Holocene normal temperature” is also the “pre-Industrial normal temperature” — the temperature prior to the year 1800. Below is a global-average temperature chart created for an IPCC (Intergovernmental Panel on Climate Change) publication released in 2000 and reprinted in an important 2009 publication, the Copenhagen Diagnosis.

Note the start of solid black line, observed temperature in the year 1800, is marked as “zero.”

The Holocene normal temperature is also the pre-Industrial normal temperature.

The Holocene normal temperature is also the pre-Industrial (pre-1800) normal temperature.
Source here, Figure 21.

As you can see from the reconstructed temperatures prior to 1800 (the fuzzy blue line), that “zero” at 1800 is pretty much the same as “zero” back through the year 500. An extended chart would show that the “zero” in 1800 is close enough to the Holocene norm as to be almost identical to it.

Unless otherwise noted, the “zero temperature change” mark — “0 ΔT (°C)” for example — on any of these charts should be read as “the Holocene norm” and also as “the pre-Industrial norm.”

This covers the first two questions above — What’s the history of life on earth and its evolution through periods of mass extinction? What’s the overview of earth climate through that period, including man’s time on earth? For more detail on each of these, see the first and second parts of this series.

Where are we headed and when?

Now let’s look at the future. This is the heart of this piece, the last in our introduction to the global warming story. Where are we going and when will we get there? In the second essay in this series, I wrote (emphasis added):

If we go to 3°C warmer, we may go to 7°C or beyond

For a reason I’ll discuss next time, if global warming is man-made — and few unbought scientists think otherwise — then 3°C warming may well be just the halfway point to the full disaster. By that I mean, because of the way the socio-political process works, the “never stop burning carbon” scenario could easily take us right past 3°C to a 7°C (12½°F) warmer world — in the worst case, by 2100 — and perhaps beyond.

That’s double the compression of Hansen’s 3°C [by 2100] scenario — it means 3°C warmer by the mid-2050s and 7°C warmer by the end of the century. The discussion of that outcome is also in the IPCC literature, the same literature Hansen used to make his mass-extinction prediction. This is their own worst-case scenario. It’s not a prediction, but it’s one of the possibilities. …

For a look at times when the earth was as hot as 7°C above pre-Industrial norms, you have to look at the Mesozoic Era and earlier …

That’s an unusual symmetry, from a +7°C spike (or more) in the deep past to a +7°C spike (or more) in the very near future. What’s different about the modern spike is the time it will take to create it. Each of those spikes in the Paleozoic Era (in orange on the second chart) occurred across tens or even hundreds of millions of years.

The temperature spike we’re creating, at our end of the chart, could well occur within the next 100–200 years. In the most chaotic situation, if governments have almost no control of populations, +7°C by 2100 becomes much more likely. No one will be able to put the brakes on carbon emissions.

Hansen says that +3°C will trigger a 20–50% extinction scenario. Think what +7°C will do. We might survive as a species (we’re awfully smart), but the world will certainly see another Great Dying.

How do we know we’re headed for 7°C global warming?

Look back at the chart immediate above (click to jump there, then click on the chart to open it larger in another window). Notice at the extreme right end, the colored lines fanning out to the edge. Each of the colored bands is a temperature projection based on various (and different) assumptions, published by the IPCC in 2000. The chart shows three of them, labeled A1FI (red), A2 (yellow), B1 (green). The IPCC has produced others, but these three are shown here.

The scenario we’re going to look at closely is “A1FI” — the most extreme. Again, click to locate it.

The document containing all of the year-2000 IPCC scenarios is IPCC Special Report: Emissions Scenarios. Here’s a link to an HTML version of the full document. And here a link to a PDF of the “Summary for Policymakers” chapter. And this is the Wikipedia page on the document. The document is usually referred to as “SRES”.

IPCC SRES scenarios form a baseline set of projections for most of the later IPCC literature, so you’ll see them referred to a lot. SRES scenarios are grouped into four families, based on differing assumptions about global integration and cooperation (or not), world population increase (or not), and so on.

Keep scenario A1FI in mind, part of the “A1”  family.  (“FI” stands for “fossil intensive,” heavier reliance on carbon.) Here is a brief description of all four families. IPCC attempted to cover all the options with this set (but they missed two):

A1 storyline and scenario family: a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and rapid introduction of new and more efficient technologies.

A2 storyline and scenario family: a very heterogeneous world with continuously increasing global population and regionally oriented economic growth that is more fragmented and slower than in other storylines.

B1 storyline and scenario family: a convergent world with the same global population as in the A1 storyline but with rapid changes in economic structures toward a service and information economy, with reductions in material intensity, and the introduction of clean and resource-efficient technologies.

B2 storyline and scenario family: a world in which the emphasis is on local solutions to economic, social, and environmental sustainability, with continuously increasing population (lower than A2) and intermediate economic development.

More on these scenario families here. Do you notice what’s missing? All of there scenario families assume some carbon mitigation. No scenario is a “Do nothing; continue as before” scenario. And none is a “Use even more carbon” scenario.

Six scenarios from these families were used by the IPCC to make sample global warming predictions through 2100. The prediction data for these six scenarios is below (source).

Note that here the reference baseline (“zero”) is the “1980–1999 average.” To convert to “zero” = the pre-Industrial norm, add approximately 1°C to each number in the table. (The generally accepted global warming number for “today” is about +1°C above the pre-Industrial norm.)

Temperature increase ranges of all six IPCC scenarios. A1FI is the last scenario listed. (Add about 1°C to each number for the increase from the pre-Industrial norm.)

Temperature increase ranges (°C) for six IPCC scenarios. A1FI is the last scenario listed.
(Add slightly less than 1°C to each number to get the increase from pre-Industrial norms.)

A1FI, the least mitigated of the SRES scenarios, is the last one listed. After adding +0.8°C for the rise from 1800 through 1999, the A1FI probable increase above the pre-Industrial norm is between +3.2°C and +7.2°C. The best estimate (most likely) temperature increase from this scenario is almost +5°C. (The same information is shown graphically here (lower chart), with the baseline year moved back to 1800. Source is the IPCC Third Assessment Report, published in 2001.)

We’re looking at the most extreme scenario because nothing is being done about carbon

As you can see from the chart and from the table:

▪ A1FI is the most extreme scenario developed by the IPCC.
▪ A1FI could get us to +7°C by 2100, even with its built-in carbon mitigations.
▪ A1FI assumes that the world will try to get off of carbon and onto alternatives, but more slowly than other scenarios. It assumes we’ll make a real attempt, one that actually reduces emissions.

Yet we’re not getting off of carbon. We’re not even trying to get off of carbon. We’re only appearing to try. Regarding Obama’s latest climate initiative, comments like this are easy to find:

Obama’s fracked-up climate strategy will guarantee global warming disaster
Fatally flawed energy policies and inadequate emissions pledges cannot prevent dangerous climate change

… [T]he new climate strategy remains fatally compromised by Obama’s unflinching commitment to the maximum possible exploitation of fossil fuels – a contradiction that has set the world on course to trigger unmitigated catastrophe in coming decades.

Again, we’re in the “third carbon era” per Michael Klare, the age of the exploitation of unconventional, hard-to-get-at carbon, and we show no desire to stop that exploitation.

Next bottom line — A1FI is the SRES scenario in which we get off of carbon, just slowly. But what if we never try? If we never even try and A1FI is a reasonable prediction, +7°C — and Hansen’s mass extinction — is a certainty.

What climate scenario are we actually on?

Can we confirm that A1FI is the path we’re taking? The Emissions Scenarios report was written in 2000, which is why the solid black line, showing observed changes, stops there.

But we’ve had a number of years in which to add observations. So here’s an update, one of many we could offer. In 2009, information from previous IPCC assessment reports (the third, or “TAR”, in 2001; the fourth, or “AR4”, in 2007) was combined and updated for the Copenhagen climate conference of 2009. The resulting document, the Copenhagen Diagnosis, is both readable and informative — and beautifully produced; take a look if you get a chance. We’ve already referred to it here.

The chart below shows several of the IPCC scenarios, again projected out from year-2000, overlaid with observations of CO2 emissions predicted by the scenarios. Note that A1FI is one of them, the red line.

Figure 1 from the Copenhagen Diagnosis, showing that the path we're on is indeed A1FI

Figure 1 from the Copenhagen Diagnosis, showing that the path we’re on is indeed A1FI

We’re smack in the middle of the A1FI range by this measure as of summer 2008 readings. Since then we’ve had the summer of melting Arctic ice and recent news that this is the hottest decade on record.

2010 ended the hottest decade on record

2010 ended the hottest decade on record (source)

I don’t see a reason to assume that A1FI is unlikely. Do you?

Last bottom line — A1FI puts us on track for as much as +7°C by 2100. And we’re on track for A1FI based on most recent observations.

Is it hopeless? Can we stop? If we don’t, will man survive?

I’ll take up all of these questions in detail later, but for now, the answers are No, Yes and Yes.

It’s not hopeless if we act, especially if we act before the window of opportunity closes. If Hansen is correct (above), that window closes at +3°C. We’ re at +1°C (more or less), with another +1°C in the pipeline. (The coming IPCC assessment report, AR5, will tell us more about that.) I’m worried that when +1.5°C is present and the same is in the pipeline, we’re in trouble. But we’re not there yet. Stay tuned.

We can stop. It will take dislocations at this point, and we’ll have to counter the big money people (carbon criminals) and their enablers and defenders in politics and the press, but it can be done.

We have obvious urgency on our side and an exponentially growing public awareness. That public awareness — fear if you will, even panic — is one of our best friends. And the climate is making the case for us as well. I’m watching Arctic ice this summer; I’ll bet I’m not alone.

I think man will survive, even if the globe warms to near impossible temperatures. There will be a place for us, even if it’s far north or far south. And our big brains didn’t evolve for nothing. We’re very good at survival; I think we will again.

More in a bit. I want to see what IPCC AR5 says. In the meantime, Courage, as Alan Grayson, a fighter, always says. Or as I like to say, “Block to the whistle. Tackle to the ground. Play to the end of the game.” You never know when events will hand you the perfect opening, and victory can be yours.

[Update: Typos corrected, including immediately above — Yes, we can stop.]


To follow or send links: @Gaius_Publius

Gaius Publius is a professional writer living on the West Coast of the United States.

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