Temperature Increases

One of the most significant indicators of global climate change is an increase in the global average surface temperature. Not only is 2006 the warmest on record for the contiguous United States, as well as tied for 5th warmest year on record globally, but other studies indicate a continued (at least century-long) warming trend, and a projected continued increase in global average surface temperature going forward.

According to estimates from the National Climatic Data Center, the largest global archive center of weather data, the global average of land and sea surface temperatures for January-December 2006 was tied for the fifth warmest on record. The World Meteorological Organization, a Specialized Agency of the United Nations system, reported that the temperature increase in the past 30 years greatly exceeds increases in previous decades. The study, based on climatic datasets maintained by the UK and U.S., finds that the temperature increase (measured as an increase over the mean between 1961 and 1990) was twice as large in the Northern Hemisphere as in the Southern Hemisphere (0.53 degrees C vs. 0.27 degrees C).

Implications: The events depicted above are in accordance with trends over the past century. Moreover, the United Kingdom’s Meteorological Office predicts that 2007 will be the warmest year ever as temperatures will be bolstered by the El Niño that emerged in the eastern Pacific Ocean in 2006, which is anticipated to exacerbate the warming trends experienced in 2006.

  • Hansen, James; Sato, Makiko; Ruedy, Reto; Lo, Ken; Lea, David W; and Martin Medina-Elizade. "Global Temperature Change." Proceedings of the National Academy of Sciences 103(39): 14288-14293 (26 September 2006).

The Earth has warmed 0.8 degrees C in the last century, having increased 0.2 degrees C per decade within the last 30 years. Using paleoclimatic data gathered from climate proxies as well as global temperature records, Hansen et al. suggest that temperatures in the western Pacific Ocean are now within roughly 1 degree C of the maximum temperature ever experienced during the last one million years. Moreover, the scientists suggest that the warming differential between the western and eastern Pacific regions may be making an increasing contribution to the strength of El Niño, especially those that occurred in 1983 and 1998. They note that species extinctions are already occurring today and will become even more likely as a result of future warming. A warming of 3 degrees C, the scientists wrote, could result in the extinction of roughly 60 percent of all species. In addition, drawing information from the Middle Pliocene, an era about three million years ago when temperatures were 2 to 3 degrees C warmer and sea level was 25-35 meters higher than today's level, Hansen et al. suggest that warming greater than 1 degrees C will constitute a "dangerous" level of warming.

Implications: Avoiding dangerous human interference with the climate is the objective of the United Nations Framework Convention on Climate Change. The Hansen et al. study suggests that virtually any additional increase in global temperature represents a “dangerous” level. Because global temperature is currently increasing approximately 0.2 degrees C per decade, and there is considerable infrastructural inertia (i.e., it will take decades to develop viable alternatives to fossil energy, replace car fleets, build new buildings and industry, etc.), this study implies that we must act soon and with considerable stringency to avoid major damages.

Despite modelers' best efforts to project future warming, model results could be altered for several reasons, such as because of the feedback from changes in the terrestrial sinks of carbon dioxide and methane (for example, increased emissions resulting from the melting of permafrost); the decline in the ocean sink (as algal growth precludes CO2 absorption or ions from calcium carbonate-based shells are released and the ocean becomes more saturated with CO2); and/or changes in albedo (from loss of snow and ice cover).

Scheffer et al. analyze past feedbacks and employ a model to come up with a potential range of positive feedbacks. They find that an extra 15 percent to almost 80 percent warming should be added to future projections as a result of taking potential feedbacks into account. Torn and Harte’s analysis corroborates this, finding that current models underestimate critical positive feedbacks of CO2 and methane. They suggest that the equilibrium temperature change associated with a doubled CO2 concentration should be revised upward from 1.5 to 4.5 degrees C to 1.6 to 6 degrees C warming. Torn and Harte’s analysis relies on ice core data and known climatic relationships which demonstrate a sizeable, long-term feedback that is not usually included in standard models. They are particularly concerned about permafrost thawing, which emits methane and carbon dioxide and changes soil carbon storage.

Implications: If proven correct, these studies’ results suggest the potential for a significant amplification in warming, as well as an exacerbation of deleterious regional climate impacts (e.g. permafrost thawing has already caused ecological and infrastructural damage). This, in turn, suggests both a more limited time to forestall climate change, and a need to rapidly improve global climate adaptation programs.