There is less than a 1-in-27 million chance that Earth's record hot streak is natural

פורסם: 20 בינו׳ 2015, 11:07 על ידי: Sustainability Org
by Andrew Freedman, 16/1/2015

Although it may not have been warm where you live, scientists announced Friday that 2014 was the Earth's hottest year since record-keeping began in 1880. The climate milestone was made possible in large part by exceptionally mild ocean temperatures and above-average temperatures on most continents.

Remarkably, the warmth came without the assistance of an El Niño event in the tropical Pacific Ocean. These events are naturally occurring ocean and atmospheric cycles that tend to boost global temperatures. Previous El Niños have been responsible in part for the prior warmest years, such as 1998 and 2005, according to data from the National Oceanic and Atmospheric Administration (NOAA).

The lack of an El Niño event indicates that such an event is no longer required to push the planet into a record warm year. Like a basketball game taking place on a court with a steadily rising parquet floor, climate change is making it possible to dunk the ball more often and set temperature records.

Temperatures Since 1880

Global average surface temperature anomalies since 1880, showing 2014 as the warmest year on record.

Image: Bob Al-Greene/Mashable

The records, which NOAA and NASA jointly announced on Friday morning despite their independent methods of data analysis, may signal that the rate of global warming, as measured by surface air temperatures, has begun to speed up again after a relative slowdown during the past 15 years or so.

According to NOAA, the average temperature across global land and ocean surfaces was 1.24 degrees Fahrenheit, or 0.69 degrees Celsius, above the 20th century average, beating the previous record warm years of 2005 and 2010 by 0.07 degrees Fahrenheit.

NOAA scientists found that record warmth was spread around the world, including Far East Russia, western Alaska, the western United States, parts of interior South America, most of Europe and parts of northern Africa, and eastern and western coastal Australia.

Notably, global average sea surface temperatures were at an all-time high in 2014, surpassing the previous records of 1998 and 2003 by 0.09 degrees Fahrenheit, or 0.05 degrees Celsius. Huge swaths of oceans were record warm, including much of the northeastern Pacific around the Gulf of Alaska, the central to western equatorial Pacific, large swaths of northwestern and southeastern Atlantic, most of the Norwegian Sea, and parts of the central to southern Indian Ocean, NOAA said.

Long odds that this isn't due to global warming

Nine of the ten warmest years have occurred since the year 2000, with 13 of the 15 hottest years on record globally all occurring during just the past 15 years, based on NOAA data.

The odds of this happening by chance — that is, rather than due to a combination of manmade pollution and natural climate variability — are less than 1-in-27 million, according to the climate research and journalism group Climate Central. Without global warming, one would expect warm and cold years to occur randomly over that period.

A separate analysis from the University of South Carolina and cited by the Associated Press found that the odds that nine out of the 10 warmest years would occur in the past decade by chance alone are about 650 million to 1.

The last year with temperatures below the 20th century average was 1976, the bicentennial of the U.S., and the year that the first “Rocky” movie hit theaters. This means that if you are younger than 38 years old, you've never experienced a year in which the global average surface temperature was below average.

According to the Union of Concerned Scientists, an environmental advocacy group, that works out to about 65% of the global population that has never experienced an average or below average year, and about half of the U.S. population.

The last month with cooler-than-average global temperatures was February of 1985, which was the month the movie "The Breakfast Club" hit theaters. This means that the planet has been warmer than average, and in many cases record warm, for an extraordinary 358 straight months, or almost 30 years.

Why this record matters

The announcement does not come as a surprise, considering the Japan Meteorological Agency announced that 2014 was the warmest year on record in its data set last week, even though each science center uses slightly different methods to analyze global temperatures. And throughout 2014, monthly temperatures repeatedly exceeded historical benchmarks.

El Niño Warm Years

Chart showing that El Niño years tend to be among the warmest (red bars), but 2014 was record warm with no El Niño present.

Image: WMO

September, for example, had the highest global average ocean temperatures on record, for any month, since 1880, according to NOAA, with a global average temperature of 61.1 degrees Fahrenheit. This was warm enough to set another milestone that had already been set two previous times this year; the average global sea surface temperature was so warm in September that it broke the all-time record for the highest departure from average for any month since 1880, at 1.19 degrees Fahrenheit above average.

The significance of an individual year in the context of the planet's climate system is relatively small. It is the long-term trend that so concerns climate scientists, who say that unless emissions of greenhouse gases such as carbon dioxide and methane are not drastically curtailed in the next few decades, the world will see warming of far greater than 2 degrees Celsius, or 3.6 degrees Fahrenheit, compared to preindustrial temperatures.

That is the level of warming that world leaders have agreed would be "dangerous" based on a 1992 U.N. climate treaty.

"For scientists, this year is simply one more to add to our long record of a warming planet. For each of us as individuals, though, this year is a reminder that our planet IS warming — that climate change is no longer a concern for future generations, it is happening here and now," said Katharine Hayhoe, a climate scientist at Texas Tech University. She said the signs of warming are evident not just in thermometer data, but in more than 26,000 "climate indicators," ranging from rising sea levels to changes in plant blooming times.

1976 Last Cold Year

1976 was the last year with global average surface temperatures below the 20th Century average.

Image: Bob Al-Greene/Mashable

If we continue on our current emissions path, we're already headed for warming of up to 9 degrees Fahrenheit by 2100, which few climate scientists argue would be anything other than catastrophic, because of the drastic rise in sea levels, heat waves, species extinctions and shifts in rainfall that would result.

There are, of course, limits to what the instrument record can tell us. We've only been keeping thermometer records since 1880, and satellites have only been measuring near-surface atmospheric temperatures since the mid-1970s.

However, painstaking climate research taking place everywhere from high atop the Greenland ice sheet to the dark depths of the Atlantic Ocean, where corals contain clues of past climates, has shown that the Earth is now the warmest it has been since at least 4,000 years ago.

Not coincidentally, the level of carbon dioxide in the air, as of early January, was about 400 parts per million, which is the highest in all of human history.

Climate scientists said the record is another signpost of a warming planet.

"Viewed in context, it underscores the undeniability that we are witnessing, before our eyes, the effects of human-caused climate change," said Michael Mann, the director of the Earth System Science Center at Penn State University. "It is exceptionally unlikely that we would be seeing a record year, during a record warm decade, during a multi-decadal period of warmth that appears to be unrivaled over at least the past millennium — if it were not for the rising levels of planet-warming gases produced by fossil fuel burning."

Eric Steig, a professor at the University of Washington, says the 2014 record helps further discredit the idea that global warming had paused since a record warm year in 1998, which was attributed in large part to an El Niño event in the tropical Pacific Ocean.

"In light of the frequent claims of their being a "pause" or slowdown in global temperature, the 2014 data provides a lesson in statistics. It will hopefully remind people what we've always known — what the textbooks have always said — that ones must use more than a decade or even 15 years of data to say anything about climate trends," he told Mashable in an email.

"As many of us have said, choosing 1998 as a start point — as those advocating for a "pause" have done — is scientifically unjustified. With a couple years more data, it is easy to demonstrate once again that we were right. It is not a surprise that the last 15 years — from 2000-2014 inclusive — show a faster rate of rise than the 1998-2012 trend, though it's equally unscientific to focus on this 15 year period as any other short period."

"In any case, global warming continues apace. Did anyone really think it would be otherwise?"
"In any case, global warming continues apace. Did anyone really think it would be otherwise?"

Surface data versus satellites

Climate skeptics often point to the satellite-based temperature record as a more accurate measure of Earth's temperature, since surface stations can be affected by urban heat island effects and other biases. NOAA scientists looked at satellite-based records for the lower and middle troposphere, which is the layer of the atmosphere where most weather occurs, as well as the stratosphere, which is the layer above it. These temperatures did not set new milestones.

For example, the 2014 global average temperature for the lower troposphere (roughly the lowest five miles of the atmosphere) was third-highest in the 1979-2014 record, NOAA said, according to the University of Alabama at Huntsville (UAH). Lower tropospheric temperatures were the sixth highest on record as analyzed by the Remote Sensing Systems (RSS).

Meanwhile, temperatures in the lower stratosphere, about 10 to 13 miles above the surface, were the 13th-lowest in the 1979 to 2014 record from UAH, and 13th-lowest in the RSS data set as well. Cooling temperatures in the stratosphere are expected in a world that is warming due to the buildup in greenhouse gases, as more heat is trapped in the lower atmosphere.

Richard Alley, a geosciences professor a Penn State, told Mashable that satellite data is simply not as valuable as surface temperature data for measuring global warming.

"As to satellites, they data are quite difficult to interpret in a qualitatively accurate manner (there is a long history of corrections of past shortcomings to improve the data products), and the data are not the temperature that most of us live in and grow our food in down here at the surface, but instead some moderately complicated average of conditions above us somewhere in the atmosphere (much better definitions can be given, but the satellites measure some weighted average up there rather than the surface down here)," he said.

"The satellite data are certainly interesting, and can be used scientifically in many ways, but in my experience most people are more interested in the temperatures down here."

Separately, Eric Steig, a professor at the University of Washington, told Mashable that satellite data's main flaw is that it doesn't tell us much about the changing climate where we live — that is, at the surface.

"We live on the surface, and the surface temperature records are the most global and longest term record we have," he said. "The satellite records measure something different — not the surface, where we live but averages over a substantial vertical part of the atmosphere. The records are short, and subject to greater uncertainties than the surface temperature data."