In the comments thread of the post Is methane hydrate out-gassing going to kill us all? BilB linked to an article The Global Impacts of Rapidly Disappearing Arctic Sea Ice by Peter Wadhams, who is professor emeritus of ocean physics at Cambridge University, a sea ice specialist with 46 years of research on sea ice and ocean processes in the Arctic and Antarctic with more than 50 expeditions to both polar regions under his belt.
He worries about what is happening in the Arctic, and after revisiting my post Reconciling estimates of climate sensitivity, I worry too. Not so much about the extinction of the human race, or about abrupt catastrophic climate change, rather how the earth system is going to end up in the long term after we extract much of carbon sediments deposited over hundreds of millions of years and inject them back into the atmosphere within the space of about a century.
As exhibit A to get us going, here is a graph, obviously smoothed, to show that something is happening:
It’s Pew Centre graph I had on file from 2006, compiled from data from official sources.
I could show you one that also has solar irradiance variations, but I assure you it has no relevance.
First, what is Peter Wadhams saying about the Arctic?
The basic fact is that the sea ice is disappearing, probably by as much as 75% by volume in the last half century. Thinner ice is more susceptible to breaking up from wave action and storms, which increases the exposure of ice to water, and hence melting. Similarly increased waves make ice harder to form in the autumn.
He thinks we could have open waters in the Arctic at the peak of the summer season, usually September. This allows more heat to be absorbed by water, which is darker than ice. Such reflectivity is termed the ‘albedo’ effect. From that point, the ice-free season will no doubt expand to three to four months a year, and eventually to five months or more.
Wadhams links to other research which found that the Arctic albedo effect is 25% as large as that due to the change in CO2 during the period 1979 to 2011.
A similar issue is at work with snow cover on Arctic land, as this graph shows:
Today snow cover loss in Arctic lands amounts to several million square miles. Run-off from the melting snow and the rivers now flows through warmer lands, yielding warmer input to the ocean.
Wadhams calculates the magnitude of this effect as similar to the ocean albedo effect above.
Then, he says, the warmer atmosphere over the Arctic holds more water vapour, as much as 20% more. Water vapour is the biggest factor of all in the greenhouse effect.
Then he talks about melting in Greenland, advising that:
- Greenland is now the largest single contributor to global sea level rise, its melting ice cap adding some 300 cubic kilometres (72 cubic miles) of water per year to the ocean.
I didn’t know that, I thought thermal expansion was still the biggest. Sooner or later, however, ice sheet decay was always going to be the main game. Over the next few centuries I understand more melting is likely to come from West Antarctica than from Greenland.
Finally, Wadham comes to the biggest worry of the lot as he sees it, the release of seabed methane from the continental shelves of the Arctic Ocean. He fears that a pulse of up to 50 gigatons of methane, some 8 percent of the estimated stock in the Arctic sediments, “could be released within a very few years, starting soon” giving in short order a boost of one degree Fahrenheit to global warming. He says that the worry is the continental shelves around the East Siberian, Kara, Laptev, and Barents seas which are only 130 to 300 feet deep. They used to be covered by ice, but are now exposed to direct warming. He says:
- This release is already causing global methane levels to rise after being flat through the early years of this century.
Other scientists disagree finding other sources most likely, but he says the ones who worry about methane are those who have actually worked on observations.
Then, he says, permafrost could yield as much again.
Obviously I can’t arbitrate on the methane matter, but longer term risk must surely remain, and there is plenty there other than methane to worry about.
- A 2011 study, for example, found that if the Arctic were ice-free for one month a year plus associated ice-extent decreases in other months then, without taking cloud changes into account, the global impact would be about 0.2ºC of warming. If there were no ice at all during the months of sunlight, the impact would close to 0.5ºC of global warming.
But his stunner was this.
Recent reviews of climate sensitivity (the warming that would result from a doubling of atmospheric greenhouse gas levels) showed a likely value of about 4°C, with a lower limit of about 3°C. However, no account was taken of “slow” feeedbacks:
- such as the decay of large ice sheets, changes in the carbon cycle (changed efficiency of carbon sinks such as permafrost and methane clathrate stores, as well as biosphere stores such as peatlands and forests), and changes in vegetation coverage and reflectivity (albedo).
There is plenty to worry about what is happening in the Arctic. James Hansen did take those issues into account in his 2011 paper Earth’s Energy Imbalance and Implications, using paleoclimate data to enhance information from climate observations and models.
Hansen’s treatment is complex, but he gives four categories of climate sensitivity. When secondary longer-term feedbacks are taken into account Earth System Sensitivity (ESS), which can play out over millennia, is more likely to be around 6°C. As a consequence he repeated his 2007 recommendation that we reduce atmospheric levels of CO2 to 350ppm as soon as possible for a safe climate.
- What is needed today is a widespread global campaign to actually remove carbon dioxide from the atmosphere using techniques like direct air capture. In my view, initiatives to devise economically acceptable methods for carbon dioxide removal from the atmosphere should be the most important concern of science and technology. The success of these efforts will mean the difference between the prospect of a positive future for mankind and the certainty of a descent towards climate-driven chaos.