We had all better hope these scientists are wrong about the planet’s future
21 March, 2016
This story has been updated.
The research invokes collapsing ice sheets, violent megastorms and even the hurling of boulders by giant waves in its quest to suggest that even 2 degrees Celsius of global warming above pre-industrial levels would be far too much. Hansen has called it the most important work he has ever done.
The sweeping paper, 52 pages in length and with 19 authors, draws on evidence from ancient climate change or “paleo-climatology,” as well as climate experiments using computer models and some modern observations.
“I think almost everybody who’s really familiar with both paleo and modern is now very concerned that we are approaching, if we have not passed, the points at which we have locked in really big changes for young people and future generations,” Hansen said in an interview.
The paper, according to Ferreira, was subject to “major revisions in terms of organisation, title and conclusions.” It also now has two additional authors.
Most notably, perhaps, the editorial process led to the removal of the use of the phrase “highly dangerous,” in the paper’s title, to describe warming the planet by 2 degrees Celsius above pre-industrial levels.
The original paper’s title was “Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous.” The final title is “Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous.”
But nonetheless, James Hansen’s climate catastrophe scenario now takes its place in the official scientific literature relatively intact. So let’s rehearse that scenario, again, for the record.
Hansen and his colleagues think that major melting of Greenland and Antarctica can not only happen quite fast — leading to as much as several meters of sea level rise in the space of a century, depending on how quickly melt rates double — but that this melting will have dramatic climate changeconsequences, beyond merely raising sea levels.
That’s because, they postulate, melting will cause a “stratification” of the polar oceans. What this means is that it will trap a pool of cold, fresh meltwater atop the ocean surface, with a warmer ocean layer beneath. We have actually seen a possible hint of this with the anomalously cold “blob” of ocean water off the southern coast of Greenland, which some have attributed to Greenland’s melting.
“My interpretation is that this is the beginning,” Hansen says of these cool patches in curious parts of the global ocean. “And it’s one or two decades sooner than in our model.”
However, when it comes to both the melt rates for Greenland and Antarctica, and also these cool ocean patches, we have a very limited time span of observations. It is far from clear, yet, that Hansen’s interpretation of them will prevail, and the new study also suggests closely observing these areas in coming years.
Stratification, the key idea in the new paper, means that warm ocean water would potentially reach the base of ice sheets that sit below sea level, melting them from below (and causing more ice melt and thus, stratification). It also means, in Hansen’s paper, a slowdown or even eventual shutdown of the overturning circulation in the Atlantic ocean, due to too much freshening in the North Atlantic off and around Greenland, and also a weakening of another overturning circulation in the Southern Ocean.
The paper contains many ideas and departures, but the key one is its suggestion of the possibility of greater sea level rise in this century than forecast by the United Nations’ Intergovernmental Panel on Climate Change.
“The models that were run for the IPCC report did not include ice melt,” Hansen said in a press conference regarding the new paper Monday. “And we also conclude that most models, ours included, have excessive small scale mixing, and that tends to limit the effect of this freshwater lens on the ocean surface from melting of Greenland and Antarctica.”
Michael Mann, a Penn State university climate scientist familiar with the original study, commented, “Near as I can tell, the issues that caused me concern originally still remain in the revised manuscript. Namely, the projected amounts of meltwater seem unphysically large, and the ocean component of their model doesn’t resolve key wind-driven current systems (e.g. the Gulf Stream) which help transport heat poleward. That makes northern hemisphere temperatures in their study too sensitive to changes in the Atlantic meridional overturning ocean circulation,” the scientific name for the ocean circulation in the Atlantic that, the study suggests, could shut down.
However, another Penn State researcher, glaciologist Richard Alley, said by email that “though this is one paper, it usefully reminds us that large and rapid changes are possible, and it raises important research questions as to what those changes might mean if they were to occur. But, the paper does not include enough ice-sheet physics to tell us how much how rapidly is how likely.”
If you dig deep enough into the Earth’s climate change archives, you hear about the Palaeocene-Eocene Thermal Maximum, or PETM. And then you get scared.
This is a time period, about 56 million years ago, when something mysterious happened — there are many ideas as to what — that suddenly caused concentrations of carbon dioxide in the atmosphere to spike, far higher than they are right now. The planet proceeded to warm rapidly, at least in geologic terms, and major die-offs of some marine organisms followed due to strong acidification of the oceans.
Can’t give the bad news without a good dose of hopium