Laura Nielsen for Frontier Scientists –
The year 2013 was the fourth warmest year on record, according to the National Oceanic and Atmospheric Administration’s National Climate Data Center. 2013 tied with 2003 in NOAA’s record, which details global average temperatures all the way back to the year 1880.
“Including 2013, 9 of the 10 warmest years in the 134-year period of record have occurred in the 21st century. Only one year during the 20th century—1998—was warmer than 2013.”
The combined land and ocean surface temperature average might be a little surprising to many on the eastern side of the contiguous 48 States’ midline, where folks have been shivering through a cold January. It’s probably less surprising to Alaskans; there, the January temperature was nearly 15°F above normal.
Temperatures in the United States have seemed odd, yet no state set a monthly record for January cold. Though it’s been especially cold in New England, this winter’s cold temperatures are fairly unremarkable compared to winters from past decades.
Though it can be hard to remember, the United States contains only 2% of the surface of the globe. In much of the world, above-average annual temperatures prevailed.
Weather | Climate
Rick Thoman, climate scientist and service manager for the National Weather Service, Alaska region, explained that “On the climate scale, which is defined to be several decades long,” something like a two month cold snap “Is just one data point. When we talk about climate change we are talking about those statistics over several decades’ change. So individual seasons like this don’t really tell us much about climate change.” Weather is always variable, and there are “Many ways the atmosphere can be,” – it’s a riotous place. “One day, one cold snap, one snow storm in May tells us nothing about climate.” You need long-term data. Thoman noted: “Most of an adult human lifetime is climate.” So, “You have to look at all of the seasons over those several decades to be able to made statements about climate.”
Examining the data, we can see an upward linear trend: Earth continues to face rising temperatures. Variable weather continues to draw fluctuating peaks and valleys on the average temperatures graph, but overall the rise in global temperatures is apparent.
At present, there is more carbon dioxide in Earth’s atmosphere than there has been at any time during the last 800,000 years. And levels are rising. Actions like burning fossil fuels pump more carbon dioxide into the atmosphere. There, CO2 joins other greenhouse gasses in trapping heat within Earth’s atmosphere.
If you encounter someone who insists that global warming stopped in 1998, point them to global temperature averages. Yes, 1998 was a very warm year. Still, it is one point among many showing a linear increase in temperatures – our planet is growing warmer.
1998 was a particularly warm year because it coincided with a particularly strong El Niño.
2013 was also a warm year, and it did not coincide with the increased temperatures that go hand-in-hand with El Niño.
El Niño is a key driver of hotter years. During El Niño events, ocean temperatures in the central and eastern Pacific Ocean near the equator are unusually high. Warm ocean waters in the Eastern tropical Pacific tend to encourage warm air temperatures and can impact weather across the globe.
Normally, the Equatorial Pacific maintains cold ocean temperatures in the East off of South America’s western coast. Trade Winds blow toward the West, pushing warm surface waters toward Indonesia. Because of how water cycles, cold water from the deep ocean comes up to the surface in the East near South America. Rain tends to occur over warm water, making it rainy in the West, cool and dry in the East.
During El Niño, Trade Winds weaken, and fail to push normal amounts of warm ocean water toward the West, and instead the warm ocean water lingers. Less rain reaches the Western Pacific and Indonesia, while more rain can be found in the Eastern Pacific – potentially leading to devastating flood or drought. The general cycle is disrupted when El Niño occurs. NOAA’s explainer page records: “The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific.” Its opposite is La Niña, in which normal conditions not only prevail but are strengthened, and very strong Trade Winds push warm surface water West, which ultimately allows the ocean to store more heat and to cycle cold deep water up to the surface in the East.
El Niño Southern Oscillation
The effects of El Niño and La Niña temperature fluctuation trends aren’t confined to the water.
Earth’s oceans and atmosphere interact; they are intrinsically related. The tropical Pacific Ocean in particular seems to have been blunting the effects of global warming by taking up excess heat from the warming atmosphere. Heat exchange between ocean and atmosphere can encourage unusually strong or weak Trade Winds, and can guide the formation of areas of high or low air pressure. Those atmospheric fluctuations that accompany El Niño highs, neutrals, and lows are referred to as the Southern Oscillation.
Taken together El Niño Southern Oscillation (ENSO) plays a major role in governing our planet’s energy balance, because heat is a form of energy and ENSO transports heat between the atmosphere and ocean and back.
“If you warm the planet – as we are – then you change the heat content of the upper ocean. That changes the sea surface temperatures and how the different ocean layers interact together,” explained Matt England, deputy director of the Climate Change Research Center at the University of New South Wales. He noted that ENSO “Changes atmospheric circulation profoundly.” Looking ahead, England believes that in the context of ongoing global warming and increased planetary heat, “Future El Niños will be phenomenally costly to society.”
El Niño Southern Oscillation ought to have its own feature article (upcoming) but we can take a brief look. Climatologists describe ENSO as having three states – neutral, negative (El Niño) or positive (La Niña). If you examine the Pacific during El Niño events – negative ENSO states – there is higher than average air pressure to the west (near Indonesia) and below-average air pressure to the east (near South America’s western coast). ENSO impacts conditions near the equator most immediately, and then its effects are felt further abroad.
“In 2013, we had a neutral ENSO, we are not far out of a solar minimum where the energy from the sun is low and we also know pollution from aerosols that cool the planet has been very high,” England elaborated. “With all these factors together, I would not have been surprised if 2013 was the fourth coolest year on record. But of course, we should not be surprised because of the extra greenhouse gases in the atmosphere.”
How do we measure global temperature?
In the simplest terms, Earth’s energy balance is governed by how much energy reaches Earth from our star, how much energy is stored here, and how much heat escapes from Earth and Earth’s atmosphere back into the cold reaches of space.
It involves an incredibly complex interplay of factors, including but not limited to: the Sun’s current strength, the position of the planet in relation to the Sun, the albedo (reflective or absorptive qualities) of Earth’s surfaces, the intermixing of atmospheric layers, the ocean’s temperature, and the measure of heat-trapping gasses that are cached away or freely roaming the atmosphere.
To measure Earth’s average temperature, data is taken from ground-based temperature measurements, from bouy-based sea surface temperatures, and – beginning in 1979 – from satellites that use microwaves to measure air temperatures in the troposphere high above our heads.
England notes that “For a long time now climatologists have been tracking the global average air temperature as a measure of planetary climate variability and trends, even though this metric reflects just a tiny fraction of Earth’s net energy or heat content.” In reality “The globe – our planet – spans the oceans, atmosphere, land and ice systems in their entirety.”
Measuring everything and everywhere is difficult, though. It is hard to establish weather stations in the most remote locations of the world, or in places like the hazardous and often icy Arctic ocean.
When NOAA takes Earth’s temperature, it uses only hard numbers from temperature measurement sites. In contrast, NASA acts to fill in the data gaps by using sophisticated computer technology – climate models. Computational science lets climatologists find a best guess: an estimation or interpolation of what temperatures exist in remote places. Meanwhile, some studies have taken estimated temperatures and further refined them. For example, Cowtan & Way focused on improving interpolations of Arctic temperatures. Their analysis showed that 2013 was warmer than 1998, despite 2013 coinciding with a neutral ENSO while 1998 gained a significant leg up on warmer world temperatures because it was a record El Niño year.
These different techniques for taking Earth’s average temperature result in different data sets. Comparing NOAA, NASA, and Cowtan & Way will show years are ranked slightly differently; however, their findings agree fairly closely and if you look past rank 5 you’ll soon see the other record warm years fall in line. The data sets face the unenviable challenge of differentiating between tiny fractions of degrees (overall, the global temperature has risen 1.4 °F [0.8 °C] since 1880).
- 1) 2010 2) 2005 3) 1998 4) 2013 5) 2003 = NOAA NCDC
- 1) 2010 2) 2005 3) 2007 4) 2002 5) 1998 = NASA GISS
- 1) 2010 2) 2005 3) 2007 4) 2009 5) 2013 = Cowtan & Way
Physicist and oceanographer Stefan Rahmstorf explains well on RealClimate: “The truly global average is important, since only it is directly related to the energy balance of our planet and thus the radiative forcing by greenhouse gases. An average over just part of the globe is not.” After all, ”The Arctic has been warming disproportionately in the last ten to fifteen years.”
You can’t separate the Arctic from its hemisphere
This year residents of Alaska (the United States’ Arctic) experienced above-normal January temperatures while their more southerly countrymen toward the East were treated to cold and snowstorms. Justin Gillis for the New York Times recorded: “The extremes in January were directly related, experts said, with the two regions falling on opposite sides of a big loop in the jet stream, a belt of high winds in the upper atmosphere that helps to regulate the climate. A dip of the jet stream into the Eastern United States allowed cold air to descend from the Arctic, while a corresponding ridge in the West allowed warm air to hover over California and to penetrate normally frigid regions to the north.”
Looking back, though, the spring of 2013 saw a very cold spring in Alaska while much of the U.S. enjoyed balmy weather. The National Weather Service’s Rick Thoman is used to such discrepancies. “There is nothing about climate change or climate variability that says that the weather will become less variable.” He added: “In fact there is some evidence, as we move into a warmer climate that – for instance – some places will cool as high latitudes,” like the Arctic, warm. “There’s increasing evidence that places at mid-latitudes … for instance Northeast United States, may experience more frequent snow storms and colder weather.” Why? Cold air that normally remained over the Arctic can get displaced South. Thoman reminded us that “Climate change and climate variability are very complex and you can have sometimes what seem to be unintuitive results,” including “More snow storms at mid-latitudes.”
How can such little numbers be tied to significant global change?
NOAA reported the 2013 global average land surface temperature was 1.78°F [0.99°C] above the 20th century (1901 – 2000) average of 47.3°F [8.5°C].
NASA’s Goddard Institute for Space Studies (GISS) determined that the average global temperature has risen about 1.4 °F [0.8 °C] since 1880. Two-thirds of that warming has occurred since 1975.
The numbers don’t seem like much, and yet they matter.
NASA’s Goddard Institute for Space Studies:
The global temperature mainly depends on how much energy the planet receives from the Sun and how much it radiates back into space—quantities that change very little. The amount of energy radiated by the Earth depends significantly on the chemical composition of the atmosphere, particularly the amount of heat-trapping greenhouse gases.
A one-degree global change is significant because it takes a vast amount of heat to warm all the oceans, atmosphere, and land by that much. In the past, a one- to two-degree drop was all it took to plunge the Earth into the Little Ice Age. A five-degree drop was enough to bury a large part of North America under a towering mass of ice 20,000 years ago.
Are you stuck in the cold shoveling, America? Or perhaps it’s hotter than you’d like? “The climate is changing, the climate is always changing,” Rick Thoman said. “On the global scale we know for certain that it is warmer than it was but on the weather scale the day in and out variability will remain with us forever.”
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- ‘Freezing January for Easterners Was Not Felt Round the World’ Justin Gillis, New York Times (Feb.2014)
- ‘GISS Surface Temperature Analysis (GISTEMP)’ GISTEMP analysis website, NASA Goddard Space Flight Center (accessed Feb.2014)
- ‘Global temperature 2013’ Stefan Rahmstorf, RealClimate (Jan.2014)
- ‘Global Temperatures’ NASA Earth Observatory : World of Change (accessed Feb.2014)
- ‘Global Temperatures Analysis – Annual 2013’ NOAA National Climatic Data Center, State of the Climate: Global Analysis for Annual 2013 (Dec.2013)
- ‘Going with the wind’ Matthew England, guest post on RealClimate (Feb.2014)
- ‘NASA Finds 2013 Sustained Long-Term Climate Warming Trend’ NASA Headquarters Press Release (Jan.2014)
- ‘What if 2013 had been an El Niño year?’ Graham Readfearn, PlanetOz, hosted by The Guardian (Jan.2014)
- ‘What is an El Niño?’ NOAA (accessed Feb.2014)