VI. Sea Level Rise

Scare stories of rapidly rising sea levels, with a magnitude exceeding many feet per century, inundating coastlines and forcing the redistribution of coastal communities as a result of increasing atmospheric levels of carbon dioxide are exaggerations of our best scientific knowledge.

The Intergovernmental Panel on Climate Change (IPCC) in its Fourth Assessment Report (AR4), projects a median sea level rise of 14 inches from its middle-of-the-road future emissions scenario (A1B). The full range of IPCC AR4 sea level rise projections, encompassing all of its various SRES emissions scenarios is 7.1 to 23.2 inches.

Range of sea level rise projections (and their individual components) made by the IPCC AR4 for its six primary emissions scenarios. Notice that the primary component is thermal expansion (red crosses), and that the contribution from Antarctica is expected to be negative (dark blue crosses) and that the contribution from Greenland is expected to be only slightly positive (light blue crosses).

The IPCC sea level rise projections stand in sharp contrast to the scare stories being put forth by Dr. James Hansen and others who contend that modest future warming will result in rapid disintegration of the Greenland and Antarctic ice sheets resulting in a sea level rise within the coming century that may exceed several meters. Hansen and his fellow believers, both prior to and following the IPCC’s release of its Fourth Assessment Report (AR4) have leveled harsh criticism of the IPCC for playing things too conservatively when it came to their projections of sea level rise. However, the IPCC lead authors staunchly defend their report’s conclusions.

For instance, IPCC AR4 lead author Dr. Richard Alley testified before the House Committee on Science and Technology, Feb. 8, 2007, concerning the state of scientific knowledge of accelerating sea level rise and pressure to exaggerate what it known about it. Dr. Alley told the Committee:

This document [the IPCC AR4] works very, very hard to be an assessment of what is known scientifically and what is well-founded in the refereed literature and when we come up to that cliff and look over and say we don’t have a foundation right now, we have to tell you that, and on this particular issue, the trend of acceleration of this flow with warming we don’t have a good assessed scientific foundation right now. [emphasis added]

The reason that Hansen and others are clamoring that the IPCC was too conservative in their estimates is a processes known as “dynamic ice changes.” Dynamic changes are the ones that are not due to the slower processes that determine ice sheet characteristics such as snowfall and ablation, but instead are due to as-of-yet unmodellable rapid changes in ice sheet outlet glaciers from processes such as basal lubrication and melting from beneath ocean-ending glacial tongues. However, the studies of dynamical ice changes are very limited in their temporal scope and thus are unreliable for assessing actual long term trends. And as we have seen for at least two major outlet glaciers in Greenland, the reported speed-ups have ended and glacial advance and thickening has begun. Whether these glacial surges will increase in the future is simply impossible to know. However, even when the IPCC attempts to take future dynamical changes into consideration in their sea level rise projections, they only arrive at small additional increases:

Further accelerations in ice flow of the kind recently observed in some Greenland outlet glaciers and West Antarctic ice streams could substantially increase the contribution from the ice sheets. For example, if ice discharge from these processes were to scale up in future in proportion to global average surface temperature change (taken as a measure of global climate change), it would add 0.1 to 0.2 m to the upper bound of sea level rise by 2090 to 2099. In this example, during 2090 to 2099 the rate of scaled-up Antarctic discharge would roughly balance the expected increased rate of Antarctic accumulation, being under A1B a factor of 5 to 10 greater than in recent years.

In other words, even when considering possible dynamical ice flow increases in the future, the IPCC still finds that they may only add about 3.9 to 7.9 inches to sea level rise estimates by the year 2100 (a far cry from Hansen’s several meters). These IPCC calculations are supported by the fact, as reported by Shepard and Wingham in Science, the current sea level rise contributed by the recent rate of ice loss from Greenland and Antarctica is about 0.014 inches per year or about 1.4 inches per century. So even if the current rate of dynamic ice loss increases by 10 times during the coming century, the added sea level rise over the course of a century will amount to little more than a foot. And considering (as we have shown) that natural year-to-year fluctuations in snowfall can explain the recent short-term reported increase in Antarctic mass loss, and in Greenland, some of the major glaciers that were advancing rapidly have suddenly slowed, there is little reason to think that significant increases in dynamical ice flow will be instigated anytime soon, if at all.

References:

Shepard, A., and D. Wingham, 2007. Recent sea-level contributions of the Antarctic and Greenland ice sheets. Science, 315, 1529-1532.

Intergovernmental Panel on Climate Change, 2007. Fourth Assessment Report. Chapter 10, Global Climate Projections.

VII. Summary

Climate change is currently ongoing in the earth’s polar regions. In fact, it has been seemingly forever. Key to current policy initiatives is the “attribution” question – whether the change is due to anthropogenic alterations to the earth’s atmosphere composition or primarily to ages old natural fluctuations beyond human control.

Of primary interest is the ongoing impact. And here, there is good news. The ice cap which covers Greenland and which contains enough water to raise global sea level some 23 feet is slow to change. Currently, the vast majority of Greenland’s glaciers have likely not retreated beyond their historical limits established in the 1950s—a period not marked by an unusual rate of sea level rise. Several major outlet glaciers that a few years ago were retreating rapidly and dumping an extra 43 Gt/year of ice into the sea (>40% of Greenland’s ice input total increase since 2000) have dramatically slowed and are regaining their equilibrium.

In Antarctica, climate models backed by long-term observations suggest that with a warming climate, Antarctica will gain snow and ice as an increase in precipitation is projected there. This will lead to a negative contribution to future sea levels from the Antarctic continent as a whole. The most scientifically-sound projections, made by the IPCC in their 2007 Fourth Assessment Report, are for a median sea level rise of 14 inches by the year 2100. This is a full order of magnitude less than the alarmist predictions by certain prominent scientists. Predictions of runaway greenhouse warming from methane released by permafrost melting have been shown to be improbable and without past precedent. And the very existence of polar bears today is proof of this species’ ability to adapt to climate changes, including conditions of significantly higher temperatures and reduced sea ice. For at least two protracted periods several thousand years in length the Arctic environment of the polar bear has been warmer and more ice free than the current one.

Many of these facts are not found in the mass media or in alarmist claims. In those settings, they are forgotten or ignored. But these facts are real, and they are readily available in the scientific literature—oftentimes directly available via the World Wide Web, not even requiring a visit to repository library. These facts tell a story with which many people are unfamiliar, a story that recognizes that the earth’s climate is changing, that a variety of human activities to some degree have a role in the changes, and that future climate changes will be modest – possibly even cooling. This contrasts with the scare stories that dominate the major media outlets portending immediate, large-scale ecological disruptions and social upheavals as a result of human-induced climate changes stemming from our energy uses.

It is important to explore the scientific knowledge that lies beneath the surface of many media reports; to investigate the full story. To convince oneself that she has received the complete picture and gained a better and fuller understanding of the issues. This is the only route to informed policy decisions preventing severely negative outcomes.

It is hoped that this document brings to light important facts that are often overlooked, circumscribed and ill-reported. This document is not intended to be the final word on any of the issues included within its contents, but instead to be catalyst that fuels further investigation of these and the many other topics that make up the complex subject of anthropogenic climate change and its implications for us all.