I warn you that this description of the latest draft paper
by James Hansen and others should horrify you, if you are sane. After Joe Romm first published its sound bite
(30 degrees Fahrenheit increase if most fossil fuels are burned, 50 degrees at
higher latitudes), I delayed reading it in detail. Now that I have, I find it
builds on his (and others’) 40 years of work in the area and the latest
research to provide an up-to-date climate change model whose implications are
mostly more alarming than any I have seen elsewhere.
What follows is my layperson’s attempt to summarize and draw
further conclusions. I scant the discussion of new analyses of previous
episodes of global warming (and cooling) that allow the development of the new
model, focusing instead on the mechanisms and implications of the model. Please note that, afaik, this is the first
model that attempts to fully include the effects of methane and permafrost
melting.
It’s About CO2
The first insight in the new model I summarize as follows:
As atmospheric CO2 increases or decreases, global average temperature
increases or decreases proportionally, with a lag either way typically of a few
decades.
This increase or decrease can be broken down into three
parts:
1.
The immediate effect of the CO2 itself --
perhaps 60% of the total effect.
2.
The immediate and “over a few decades” effect of
other “greenhouse gases” , or GHGs (here we are talking particularly about the
methane in permafrost and methane hydrates on the continental shelves, released
by warming, as well as GHGs such as nitrous oxide) – perhaps 20% of the total
effect.
3.
The so-called “fast feedback” effects, in which
the released CO2 and other factors (e.g., increased albedo) lead to additional
warming “over a few decades”.
Two quick notes:
First, Hansen does not do my split; instead, he distinguishes between
the effects of CO2 and the effects of other GHGs over the medium term (about
75-25) and then separately distinguishes between the immediate overall “climate
sensitivity” and the medium-term or total “climate sensitivity” (again, about
75 % immediately and 100 % in the long term).
Second, the “over a few decades” is my interpretation of how quickly “X
times CO2” seems to match global temperature data over more recent sets of
data. Hansen might very well say that
this may or may not occur quite this rapidly, but it doesn’t matter to him
because even with a thousand-year time frame for the full effect, CO2 will not
be recycled out of the atmosphere for “few thousand years”, so we still reach
the full “climate sensitivity”.
Just to get the usual objections out of the way, Hansen is
not saying that CO2 always leads the way – on the contrary, in Ice Age
scenarios in which a certain point in a Milankovitch cycle causes extreme
winters in our northern hemisphere, leading to increased glaciation and
therefore decreased albedo and CO2 release to the atmosphere, CO2 follows other
factors. Today, however, primarily
because of fossil-fuel emissions, CO2 is leading the way.
A sub-finding, still important, is that there is a linear
relationship (again, sometimes with a lag of decades) between deep-ocean
temperature change and atmospheric temperature change (expressed as “the change
in temp at the surface is somewhere between 1.5 and 2.5 times the change in
temp of the deep ocean” – or, about 67%
of the global temperature increase goes into surface temps, 33% into deep ocean
temps). I include this because it
seems that the recent “slowdown” in global surface temperature ascent is
primarily caused by increased accumulation in the deep ocean. However, again in a relatively short time
frame, we should go back to more rapid average global surface temperature
increases, because we’re still increasing atmospheric CO2 rapidly and 2/3 of
that will start again going back into surface temps.
The Effect of “CO2 Plus” Is Bigger Than We Thought
In the past, Hansen among others has seen the effect of
doubled CO2 as somewhere in the 2-3 degrees Celsius range. Now, he sees a range of 3-4 degrees C –
apparently, primarily because he now takes into account “other GHGs”. To put it more pointedly, in my own
interpretation:
Each doubling of CO2 leads to a global temperature change of 2.25-3
degrees Celsius (4-5.4 degrees F) “over a few decades”, and to a change of 3-4
degrees C (5.4-7.2 degrees F) “over 1 or 2 centuries.”
I mention this not only because the consequences of today’s
global warming are more dire than we thought (i.e., the effects of that
warming, immediately and over the next century or two), but also because many
of us are still hung up over that “stop emissions and hold the increase to 2
degrees C” target that was the main topic at recent global governmental
summits. The atmospheric CO2 level at
the beginning of the Industrial Revolution was about 250 parts per million
(ppm), and is now at about 400 ppm. If
you do the math, that means we have baked in at least 2.2-3 degrees C of global
temperature increase already. After 15 years of inaction, that target now has
zero chance of success.
At this point, I want to do a shout-out to those wonderful
folks at the Arctic Sea Ice blog and forum.
Hansen specifically notes the data supporting melting of Arctic sea ice,
plus collapse of the Greenland and West Antarctic ice sheets, at levels
slightly below today’s CO2. He also
notes data supporting the idea that Greenland and West Antarctica can go pretty
rapidly, “in a few centuries”, iirc – I interpret “in a few centuries” as
within 250-450 years from now.
The Percent of Fossil Fuels We Need To Leave In The Ground Forever Is
Greater Than We Thought
Before I get to the consequences if we don’t leave a
percentage of fossil fuels in the ground, let’s see how the minimum amount of
fossil fuels burned before we reach “worst consequences” has changed. Today’s
estimate of total recoverable fossil-fuel reserves (coal, oil [primarily tar
sands and oil shale], and natural gas) is about the equivalent of 15,000 Gt C
(billions of tons of carbon emitted). Of
this, coal is about 7.3-11 Gt C, and the rest is split approximately
equivalently between natural gas and tar sands/oil shale. Originally, we
thought that burning 10,000 Gt C in the next century would get us to “worst
consequences”. Now, Hansen places the
correct amount as somewhere between 5,000 Gt C and 10,000 Gt C. Reading between the lines, I am placing the
range as 6,000-7,000 Gt C, with 5,000 Gt C if we want to be ultra-safe, and I’m
estimating coal as 60% of the emittable total, 20% tar sands/oil shale/oil, 20%
natural gas. Note, btw, that according
to Hansen fossil-fuel emissions have increased consistently by about 3 % per
year since 1950, including last year. At that rate, we’d reach 6,000-7,000 Gt C
in about 65-70 years.
Again, note that Hansen breaks the fossil fuels down as
coal, traditional oil/gas, and oil shale/tar sands/fracked gas, so I’m
guesstimating the equivalents.
So here’s the way it works out:
If we burn all the coal plus a very minor amount of everything else, we
reach “worst consequences.”
If we burn all of everything but coal and 33% of the coal, we reach
“worst consequences”.
If we burn 17% of the coal, 50% of the natural gas, and all the tar
sands/oil shale/oil, we reach “worst consequences”.
So this, imho, is why I agree with Hansen that allowing the
Keystone XL pipeline is “game over” for the climate, as in “worst consequences
almost inevitable”. The Keystone XL
pipeline is a “gateway drug” for tar sands and oil shale. The source (Alberta, Canada) has a large part
of the known tar sands oil, and presents similar difficulties in abstracting
and processing to oil shale. It’s the
furthest along in terms of entering the world market. If that source succeeds, as the saying goes,
once the nose of the camel is in the tent, you may expect the rest of the camel
to enter. In this case, if Alberta
succeeds in getting the Keystone XL pipeline, it is probably the case that most
of the tar sands and oil shale will be used; if not, probably not.
Right now, Alberta has no real buyers except the US, and the
US is not set up to accept the oil, nor Canada to ship it to them in bulk. The pipeline would effectively create an
infrastructure to ship it, primarily to the rest of the world, which presumably
would accept it – especially China – creating a market that allows Alberta
profitability. Alternatives are much
more costly, are susceptible to pressure from the US, and would probably not be
undertaken at all. Note that increased
shipment via truck is more costly, and would probably require major investments
in truck structure, to handle the more toxic tar-sands crude, so that it is
probably not a large-scale alternative that would make the project a
success. Likewise, trains and tracks to
the Canadian ports to ship directly to world markets would probably prove too
costly.
Now go back to the model.
It’s pretty darn likely we’ll burn 17% of the coal no matter what, and
the majority of the natural gas. Now add
the tar sands and oil shale. Worst
consequences, here we come.
The Worst Is Likelier Than We Thought, Arrives Sooner, Is Almost As Bad As
Our Worst Nightmare, And Is More Inescapable Once We Get There Than We Hoped
We’ve already dealt with “likelier than we thought”, and we
can guess from the rapidity of response to atmospheric CO2 rise and the
increase in the estimated climate sensitivity to atmospheric CO2 that it arrives
sooner than we had projected. But what is this “worst consequences almost as
bad as our worst nightmare”, and “worst consequences, once arrived, more
inescapable that we hoped”?
For us, the worst consequences are not “snowball Earth”,
locked in eternal ice, but “runaway GHG Earth” a la Venus, with the surface and
air too hot and too acid to support water or any life at all (water vapor in
the atmosphere vaporizes from the heat long before it reaches the
surface). It’s an inescapable condition,
since once the atmosphere locks in the heat, the Sun’s heat from outside trapped by the CO2 and other gases in the atmosphere balances
escaping heat from the troposphere (top of the atmosphere). Hansen’s model shows that we are still 100
million to 1 billion years from being able to reach that state, even by burning
all fossil fuels in a gigantic funeral pyre.
The worst consequence, as cited before, is therefore as
cited at the very beginning, Joe Romm’s sound bite: 30 degrees F increase globally, 50 degrees in
the high latitudes. Here’s Hansen’s take
on what that means: it will take all
areas of the Earth except the mountains above 35 degrees C “wet bulb
temperature” during their summers. That
in turn, according to Hansen, would mean the following:
In the worst-consequence world, humans could survive below the
mountains during the day outside only for short periods of time during the
summer, and there would be few if any places to grow grains.
Effectively, most areas of the globe would be Death
Valley-like or worse, at least during the summer.
Here I think Hansen, because he properly doesn’t diverge
into movement polewards of weather patterns and the effects of high water and
possible toxic blooms, underestimates the threat to humanity’s survival. Recent research suggests that with global
warming, tropic climates stretch northwards.
Thus, projections for the US (not to mention Europe below Scandinavia,
Australia, southern Africa, and southern Russia) is for extreme drought. How can this be, when there will be lots of
increased water vapor in the air?
Answer: it will be rare in falling, and far more massive and violent
when it does. The heat will bake the
ground hard, so that when it does rain, the rain will merely bounce off the
ground and run off (with possible erosion), rather than irrigating anything. Add depletion of aquifers and of ice-pack
runoff, and it will be very hard to grow anything (I suppose, mountains
partially excepted) below Siberia, northern Canada/Alaska, and
Scandinavia.
However, these have their own problems: rains too massive (and violent) to support
large-scale agriculture – which is why you don’t see farming on Seattle’s
Olympic Peninsula. The only
“moderate-rainfall” areas projected as of now, away from the sea and the
equator, are a strip in northern Canada, one in northern Argentina, one in
Siberia, and possibly one in Manchuria. Most of this land is permafrost right
now. To even start farming there would
require waiting until the permafrost melts, and moving in the meantime to
“intermediate” farming areas. Two moves,
minimal farmland, and greater challenges from violent weather. Oh, and if you want to turn to hunting you’ll
be lucky if you have an ecosystem that supports top-level meat animals, not to
mention the 90% of plant and animal species that will likely be extinct by
then. As for the ocean, forget about it as a food source, unless you like
jellyfish (according to research done for the UN recently).
In my version of Hansen's worst-consequence world, we would try to
survive on less than 10 % of today's farmland, less than 10% of the animal and
vegetable species with disrupted ecosystems, and practically zero edible ocean
species, in territory that must be developed before it is usable, in dangerous
weather, for thousands of years.
Hansen notes that one effective animal evolutionary response
to past heat episodes has been hereditary dwarfism. Or, as I like to think about it, we could all
become hobbits. However, because we are
heading towards this excessive heat much faster than in those times, we can’t
evolve fast enough; so that’s out.
What about inescapable?
Well, according to Hansen, CO2 levels would not get out of what he calls
the “moderately moist greenhouse” area for thousands of years, and would not
reach close to where we are now until 10,000-100,000 years hence. By which time, not only will we be dead, but
most of humanity, if not all.
Now, I had feared the Venus scenario, so the worst
consequences are not as bad as I thought.
However, the increased estimate for temperatures in the moderately moist
greenhouse and the wet bulb temperature consideration makes the next-worst
scenario more likely than before to end humanity altogether.
Snowball Earth: Sad Beauty of a
Sidelight
Having said all this, Hansen at least gives a beautiful
analysis of why we don’t wind up a “snowball Earth” (the opposite scenario from
a “runaway greenhouse”). He notes that
once the Earth is covered with ice, carbon can’t be recycled to the Earth via
“weathering” (absorption from the atmosphere by rocks whose surfaces are
abraded by wind and water). So volcanic
emissions and the like put more and more carbon dioxide in the atmosphere,
until the temperature warms up enough and melting of the ice begins. Apparently, evidence suggests that this may
have happened once or twice in the past, when the Sun was delivering less light
and hence heat.
Envoi
The usual caveats apply.
Primarily, they fall in the category of “I was reading Hansen out of
fear, and so I may be stretching the outer limits of what may happen, just as
Hansen may be understating out of scientific conservatism.” Make up your own mind.
I am reminded of a British Beyond the Fringe comedy skit
about WW II, suitably amended:
“Go up in the air, carbon. Don’t come back.”
“Goodbye, sir. Or
perhaps it’s ‘au revoir’?”
“No, carbon.”
And what will it take for humanity to really start listening
to Hansen, and to the science?
