Stephens: SuperFreakonomics “note[s] that sea levels will probably not rise much more than 18 inches by 2100”

From Stephens' October 27 Wall Street Journal column:

But when it comes to the religion of global warming -- the First Commandment of which is Thou Shalt Not Call It A Religion -- Messrs. Levitt and Dubner are grievous sinners. They point out that belching, flatulent cows are adding more greenhouse gases to the atmosphere than all SUVs combined. They note that sea levels will probably not rise much more than 18 inches by 2100, “less than the twice-daily tidal variation in most coastal locations.”

SuperFreakonomics: Astrophysicist Lowell Wood “notes” authoritative estimate of sea level rise is 1.5 feet by 2100. From SuperFreakonomics, Chapter 5, “What do Al Gore and Mount Pinatubo Have in Common?”:

The gentlemen of IV [Intellectual Ventures] abound with further examples of global warming memes that are all wrong.

Rising sea levels, for instance, “aren't being driven primarily by glaciers melting,” Wood says, no matter how useful that image may be for environmental activists. The truth is far less sexy. “It is driven mostly by water-warming -- literally, the thermal expansion of ocean water as it warms up.”

Sea levels are rising, Wood says -- and have been for roughly twelve thousand years, since the end of the last ice age. The oceans are about 425 feet higher today, but the bulk of that rise occurred in the first thousand years. In the past century, the seas have risen less than eight inches.

As to the future: rather than the catastrophic thirty-foot rise some people have predicted over the next century -- good-bye, Florida! -- Wood notes that the most authoritative literature on the subject suggests a rise of about one and a half feet by 2100. That's much less than the twice-daily tidal variation in most coastal locations. “So it's a little bit difficult,” he says, “to understand what the purported crisis is about.” [Pages 185-186, emphasis added]

But the 1.5 ft estimate from 2007 did not account for “changes in ice flow” currently being observed

UCS: Sea level rise projection “failed to include additional sea level rise from melting ice sheets.” The Union of Concerned Scientists stated that SuperFreakonomics “Mischaracterizes Climate Science” and listed several criticisms of Chapter 5, including the statement that Levitt and Dubner "[i]gnore a major source of sea level rise." UCS stated:

The authors maintain that sea levels can rise only 1.5 feet by 2100 (page 186). How did they arrive at that statistic? It seems they only considered sea level rise due to a warming (and expanding) ocean, but failed to include additional sea level rise from melting ice sheets.

Over the last few years scientists have gained greater understanding of how land-based glacial ice responds to warming and how much it may contribute to sea level rise. A new study using the latest climate science suggests sea levels may rise 2.6 to 6.6 feet by the end of this century depending on our emissions over the coming century. In addition, unchecked warming may at some time in the future cause the Greenland and West Antarctic ice sheets to melt completely, leading to catastrophic sea-level rise.

2007 IPCC report projected sea level rise of .6-1.9ft (.18-.59m) by 2100, but noted estimate did not “include the full effects of changes in ice sheet flow.” The IPCC stated in a summary of its 2008 Fourth Assessment Report that its range of projected sea level rise is derived from models that “do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking.” The report further stated that at the time, “understanding of these effects is too limited to ... provide a best estimate or an upper bound for sea level rise.” The chart showing the range of projections specifies that the estimates “exclud[e] future rapid dynamical changes in ice flow.”

UCS noted “major developments” since publication of IPCC's 2007 report. In February, UCS wrote, “Major developments in climate change science have been reported since the publication of the comprehensive 2007 Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC).” UCS further stated:

The IPCC (AR4) estimated global average sea level rise for the end of this century (2090-2099) compared with the end of the last century (1980-1999) at between ~0.6-1.9 feet (~0.2-0.6 meter). These projections were based primarily on thermal expansion due to ocean warming with only modest contributions from mountain glaciers, leaving the potential contributions from ice sheets covering Antarctica and Greenland unclear. Because understanding of ice sheet behavior is still evolving, future ice sheet disintegration was not included in models used by the IPCC at that time. Researchers have since examined plausible contributions from ice sheets given current understanding of accelerating ice sheet melt and other factors. New analysis indicates that meltwater from ice on land could lead to a sea level rise increase of ~2.6 feet (0.8 meter) by the end of the century; and although ~6.6 feet (2.0 meters) is less likely, it is still physically possible. As depicted in Figure 3, when increased contributions from glaciers and ice sheets are taken into account, plausible twenty-first century sea level rise is higher than IPCC estimates.

Eric Rignot: “The results gathered in the last 2-3 years” show ice sheets' increased contribution to sea level rise. Science Daily reported that Eric Rignot of the University of California-Irvine and NASA's Jet Propulsion Laboratory stated: “The numbers from the last IPCC are a lower bound because it was recognized at the time that there was a lot of uncertainty about ice sheets. The numerical models used at the time did not have a complete representation of outlet glaciers and their interactions with the ocean. The results gathered in the last 2-3 years show that these are fundamental aspects that cannot be overlooked”:

New insights reported include the loss of ice from the Antarctic and Greenland Ice Sheets. “The ice loss in Greenland has accelerated over the last decade. The upper range of sea level rise by 2100 might be above 1m or more on a global average, with large regional differences depending where the source of ice loss occurs”, says Konrad Steffen, Director of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder and co-chair of the congress session on sea level rise.

The last assessment report from the IPCC from 2007 projected a sea level rise of 18 - 59 centimeter. However the report also clearly stated that not all factors contributing to sea level rise could be calculated at that time. The uncertainty was centered on the ice sheets, how they react to the effects of a warmer climate and how they interact with the oceans, explains Eric Rignot, Professor of Earth System Science at the University of California Irvine and Senior Research Scientist at NASA's Jet Propulsion Laboratory.

“The numbers from the last IPCC are a lower bound because it was recognized at the time that there was a lot of uncertainty about ice sheets. The numerical models used at the time did not have a complete representation of outlet glaciers and their interactions with the ocean. The results gathered in the last 2-3 years show that these are fundamental aspects that cannot be overlooked. As a result of the acceleration of outlet glaciers over large regions, the ice sheets in Greenland and Antarctica are already contributing more and faster to sea level rise than anticipated. If this trend continues, we are likely to witness sea level rise one meter or more by year 2100”, he says. [Science Daily, 3/11/09]

U.S. Climate Change Science Program: Models do not capture ice sheet loss “that we are already observing.” The U.S. Climate Change Science Program stated in a December 2008 report that "[e]xisting models suggest that climate warming would result in increased melting from coastal regions in Greenland and an overall increase in snowfall. However, they are incapable of realistically simulating the outlet glaciers that discharge ice into the ocean and cannot predict the substantial acceleration of some outlet glaciers that we are already observing." In an article about the report, The Washington Post stated: “In one of the report's most worrisome findings, the agency estimates that in light of recent ice sheet melting, global sea level rise could be as much as four feet by 2100. The IPCC had projected a sea level rise of no more than 1.5 feet by that time, but satellite data over the past two years show the world's major ice sheets are melting much more rapidly than previously thought.”