by Andrew Glikson
An ice-free world isn’t impossible – even though it seems the stuff of science fiction. — Alistair Knock
Last December’s meeting of the American Geophysical Union featured three of the world’s leading climate scientists: James Hansen (NASA’s chief climate scientist), Elco Rohling (National Oceanography Centre, Southampton) and Ken Caldeira (Stanford School of Earth Science). But it was Hansen who attracted the most attention when he stated:
If you doubled CO₂, which practically all governments assume we’re going to do, that would eventually get us to the ice-free state (and) We would be sending our climate back to a state we haven’t adjusted to as a species.Reaching ice-free-Earth conditions due to the addition of a few hundred parts per million CO₂ may sound like a science fiction story. But Hansen’s statement is consistent with the natural laws of physics (the Planck, Stefan-Boltzmann and Krichhoff laws of black body radiation), with atmospheric science and with the geological record.
A planet’s surface temperature is determined by the infrared absorption/emission characteristics of its atmosphere, determined by greenhouse molecules (CO₂, CH₄, N₂O, O₃). Earth’s surface conditions (including the atmospheric pressure, temperature and gases in its atmosphere) occupy an intermediate position between those of Mars and Venus. Advanced life on Earth is controlled by the presence of water and by the carbon and oxygen cycles.
|Figure 1: CO2 with time. Andrew Glikson (with thanks to D Royer)|
Studies of the evolution of the terrestrial atmosphere based on multiple proxies (carbon isotopes in phytoplankton and in fossil soils, plant leaf stomata pores, boron isotopes, boron/calcium ratios) confirm the upper stability boundary of the Antarctic ice sheet at about 500+/-50 ppm CO₂. Other estimates suggest 615 ppm CO₂ or near-800 ppm CO₂.
With current emissions growing by 5.9% in 2010 (see Figure 2) and a corresponding rise of temperature by 6.2% during the last decade (see Figure 3), Earth may be committed to an ice-free state.
|Figure 3: Percentage change in global average temperature since the 1860s by decade. World Meteorological Organization|
Climate change projections are complicated by the extreme rates of these processes. There is no precedent for such rates in the geological record, bar major greenhouse gas release triggered by methane eruptions, volcanic eruptions and asteroid impacts.
The bulk of the continents continue to heat, due to a rise in greenhouse gases, feedbacks from fires, methane release from permafrost and reduction of CO₂ intake by warming oceans.
The resultant ocean-land temperature polarity generates storms, reflected in the title of James Hansen’s book, “Storms of my grandchildren”. Similar conditions developed in November 2010 as north Siberia and Canada warmed to above 4°C relative to 1951-1980 while snow storms occurred in the North Atlantic.
Figure 4: Surface temperature Goddard Institute for Space Studies, NASA
The current consequences of polar temperature rises by 4°C and higher (see Figure 4) for the Greenland and the Antarctic ice sheets are shown in Figure 5. Between 2002 and 2008 a total of near-2500 billion tons of ice was lost while the projected rate of mass loss near-doubled over the period.
|Figure 5: Ice mass changes|
Good planets are hard to come by.
Andrew Glikson is Honorary Professor at the Geothermal Energy Centre of Excellence, The University of Queensland, and a Visiting Fellow at the Australian National University.
This article was originally published at The Conversation. Read the original article.RELATED POSTS