Temperature record (mean surface temperature)
The temperature record refers to the systematic collection and analysis of Earth's surface temperature data over time, primarily conducted by various international scientific institutions such as NASA's Goddard Institute for Space Studies. Since formal records began in 1880, this data has shown a significant upward trend in global temperatures, highlighting the phenomenon of global warming. The average global temperature has risen by approximately 1.4°F (0.8°C), with most increases occurring after 1975. Despite a general warming trend, there has been a noted slowdown from 1998 to 2012, prompting scientists to investigate potential causes, including changes in ocean currents and atmospheric conditions.
Various institutions compile temperature data from thousands of meteorological stations worldwide, allowing for a comprehensive analysis of annual and decadal temperature changes. Although slight differences exist in their methodologies, these institutions generally agree on the warming trends observed in recent decades. The rise in temperatures is closely linked to increased greenhouse gas emissions, particularly carbon dioxide, which has risen significantly since 1880. However, scientists remain cautious in their predictions, recognizing the complexity of weather patterns and other factors that may influence temperature fluctuations. Understanding the temperature record is crucial for addressing climate change and its potential impacts on the planet.
Temperature record (mean surface temperature)
The temperature record is a record of the fluctuations in Earth’s temperature over time. Compiled by different international science institutions, including the National Aeronautics and Space Administration's (NASA) Goddard Institute for Space Studies, the temperature record shows the average temperature over the entire surface of Earth. An analysis of the temperature record reveals a steady increase in global temperatures since scientists began keeping records in 1880. Although this points to global warming, evidence suggests that the rate at which Earth is warming per decade actually slowed from 1998 to 2012. Experts are unsure why the slowdown occurred, but a possible explanation is that the equatorial Pacific Ocean entered a cold state following the El Niño of 1997 to 1998.
Overview
Scientists have been tracking Earth’s temperature record since 1880. Four international science institutions—NASA's Goddard Institute for Space Studies (GISS), the Met Office Hadley Centre Climatic Research Unit, the National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center (NCDC), and the Japan Meteorological Agency—work to compile the record. These institutions collect temperature data from thousands of stations throughout the world. Based on these data, the institutions then determine whether each year was warmer or cooler than average.
For example, GISS collects public data from 6,300 meteorological stations, observations of sea surface temperature taken from ships and satellites, and measurements from Antarctic research stations. GISS then loads the data sets into a computer analysis program. The program calculates trends in temperature differences compared to average temperatures during the period 1951 to 1980. This particular period is used because the United States National Weather Service uses a three-decade term to identity average temperatures. Furthermore, GISS began its temperature analysis around 1980, so the period from 1951 to 1980 worked best.
Because each of the four institutions analyzes its data in a slightly different way, the official records are somewhat different. However, all four institutions typically agree. For example, the records of all four institutions exhibit similar peaks and valleys in Earth’s temperature over time. Additionally, all four records show that in the last few decades, Earth has been rapidly warming, with the last decade being the warmest decade ever. According to NASA’s Goddard Institute for Space Studies, the ten warmest years on record have occurred since 1998.
Rising Temperatures
Scientists predict a long-term rise in the temperature record. Since 1880, the average global temperature has increased 1.4°F (0.8°C), with the majority of this increase occurring since 1975. The temperature has increased at a rate of 0.15 to 0.20°C per decade. In 2012, the average temperature was 58.3°F (14.6°C). This temperature is 1°F (0.55°C) warmer than the average temperature of the mid-twentieth century.
Because weather patterns cause fluctuations in average temperatures each year, scientists do not expect every year to be warmer than the previous year. However, scientists do anticipate that every decade will be warmer than the prior decade. Scientists believe this trend results from the constant increase in greenhouse gas levels in Earth’s atmosphere. Specifically, the atmosphere has been hit with increased levels of carbon dioxide, which traps heat. Carbon dioxide is released when fossil fuels are burned. From 1880 to 2012, carbon dioxide levels in the atmosphere rose from 285 parts per million to 390 parts per million.
Stalled Warming
Despite the rise in global temperatures, global warming appears to have stalled. In 1997, tropical trade winds in the Pacific Ocean weakened, which resulted in El Niño. El Niño is the warming of surface water in the eastern tropical Pacific Ocean. The name is Spanish for “the Christ child,” as the phenomenon occurs around the time of Christmas. El Niño is part of the Southern Oscillation, which is a pattern of reversing surface air pressure in the Pacific Ocean. The entire phenomenon is referred to as the El Niño/Southern Oscillation, or ENSO. Perhaps as a result of the El Niño of 1997 to 1998, global temperatures reached record numbers in 1998. Then global warming slowed. Simulations found that Earth’s warming should have continued to increase at an average rate of 0.21°C per decade from 1998 to 2012. Collected data, however, show a warming of only 0.04°C per decade.
Several possible explanations for this hiatus in global warming exist. For one, the El Niño of 1997 to 1998 may have been followed by a cold state in the equatorial Pacific Ocean that quelled global temperatures. This was likely caused by La Niña, El Niño’s sister effect. Another explanation of the hiatus is that the impact of greenhouse gases may be overestimated, thus the concern over future warming may be exaggerated. The energy output from the Sun also may play a role in the global warming halt. The Sun is believed to have an eleven-year cycle in which its energy output waxes and wanes. Around 2000, the Sun entered a lull, which may explain the halt in global warming. Another theory involves the increase in stratospheric aerosol particles, which reflect sunlight back into space. This increase may have played a role in suppressing global temperatures.
Bibliography
Carlowicz, Michael. “Global Temperatures.” Earth Observatory. NASA. Web. 8 Dec. 2014. http://earthobservatory.nasa.gov/Features/WorldOfChange/decadaltemp.php
Earth Observatory. “Long-Term Global Warming Trend Continues.” Earth Observatory. NASA. 16 Jan. 2013. Web. 8 Dec. 2014. http://earthobservatory.nasa.gov/IOTD/view.php?id=80167
“El Nino—and What Is the Southern Oscillation Anyway?!” For Kids Only. NASA. 22 Jan. 2003. Web. 8 Dec. 2014. http://kids.earth.nasa.gov/archive/nino/intro.html
“Graphic: Earth’s Temperature Record.” Global Climate Change: Vital Signs of the Planet. NASA. Web. 8 Dec. 2014. http://climate.nasa.gov/climate‗resources/9/
Tollefson, Jeff. “Climate Change: The Case of the Missing Heat.” Nature. Nature Publishing Group. 15 Jan. 2014. Web. 8 Dec. 2014. http://www.nature.com/news/climate-change-the-case-of-the-missing-heat-1.14525