Climate Change and Polar Amplification
The carbon dioxide content of the atmosphere has been steadily increasing from its preindustrial value of ~280 parts per million (ppm) (Figure) (IPCC, 2007a), and the rate of increase has significantly intensified in the past 60 years, from 0.53 ppm per year in 1957 (when measurements were started) to nearly 2 ppm per year in 2008. If this trend continues, by 2057 (perhaps the time of the next IPY) carbon dioxide values may approach 500 ppm. Furthermore, there is increasing documentation that in the geologic past, continental ice sheets grew only when atmospheric carbon dioxide values were low and retreated when values were high. Such trends are in agreement with climate change projections based on increasingly sophisticated computer simulations of climatic change.
Climate changes and their impacts have considerable spatial variability due to Earth’s interlinked and moving atmospheric and oceanic circulation patterns. Although warming of the planet as a consequence of anthropogenic carbon dioxide is happening nearly everywhere (IPCC, 2007a), it is accentuated in the high latitudes due to polar amplification caused by strongly positive snow and ice feedbacks (Serreze et al., 2009; Manabe and Wetherald, 1975). Concern about this polar amplification drove much of the research carried out during IPY, and the complex nature of Earth systems and changes will require significant and continuing investigation to foster understanding and action toward sustainability.
FIGURE The carbon dioxide (CO2) data (red curve) measured on Mauna Loa constitute the longest record of direct measurements of CO2 in the atmosphere. The black curve represents the seasonally corrected data.
SOURCES: NOAA Earth System Research Laboratory and Scripps Institution of Oceanography.
discoveries of large changes occurring in both ice sheets. Taken together, these assessments showed that the pace of ice sheet mass loss has been increasing since the end of the last century, accelerating sea level rise. As a result of research coming out of IPY, projections for the future show an accelerating trend for sea level rise by 2100, with model predictions ranging from 20 to 180 cm (Figure 3.2). The upward trend in sea level rise is primarily the result of melting of glaciers and small ice caps, and the thermal expansion of seawater due to ocean warming. The former accounts for about 30 percent of the contribution to sea level rise (Nicholls and Cazenave, 2010).
Ice sheet mass changes can be estimated using data from Gravity Recovery and Climate Experiment (GRACE), a satellite designed to measure gravity variations, which in this case are created by regional mass redistributions within the ice sheets. IPY findings from the LEGOS1 project using GRACE data provided evidence that the Greenland and Antarctic ice sheet contributions to sea level rise increased to 30 percent of the total sea level rise after 2003, compared to their smaller contribution of 15 percent of sea level change between 1993 and 2003 (IPCC, 2007a). Repeat observations of ice sheet elevations from the laser altimeter onboard ICESat-1 captured the detailed