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 CO2The 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 ThoughtIn 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 ThoughtBefore 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 HopedWe’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.
EnvoiThe 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’?”
And what will it take for humanity to really start listening to Hansen, and to the science?