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Greenhouse gas emissions drive back-to-back-to-back global surface temperature records
2016 was the hottest year on record, according to independent global surface temperature analyses from NOAA, NASA, the UK Met, and JMA. Satellite data analyses from Remote Sensing Systems (RSS) and University of Alabama in Huntsville (UAH) also confirmed that 2016 was record hot. 2014-2016 is the only period in the modern record that has yielded three straight record-breaking years in a row. Prior to the modern era, the only other period that witnessed three straight years of record breaking warming was 1939-1941, a stretch that occurred after an extended cool period. The total jump over those three years was (0.23°C). In comparison, the jump over just the two years of 2014 and 2015 alone (0.23°C) is already equal to the three year jump over 1939-41. And the jump over 2016 will take it significantly further.
Warming in 2016 was so strong that by mid-April, the Director of the NASA Goddard Institute for Space Studies was able to estimate a greater than 99 percent chance that 2016 would beat 2015 as the hottest year on record, based on January through March data alone.
This streak of record-breaking warming reflects the unabated pace of global warming seen even more clearly in the long-term data over the past several decades.
Across this current warming streak every month between May 2015 through August 2016 was the hottest version of that month since recordkeeping began in 1880, according to NOAA. July 2016 was also the hottest month in meteorological history, tied, shortly after, by August 2016. 15 of the 16 hottest years on record have occurred since 2001, according to NOAA data. The exception is 1998 which ranks 7th in NOAA's database.
The global average surface temperature anomaly in 2015 broke the previous record set in 2014 by the widest margin ever recorded, and 2014 broke the previous record (set in 2010 during an El Niño) despite occurring without a boost from El Niño.
El Niño adds small bump to warming driven by greenhouse gas emissions
While global warming is occurring rapidly in all parts of the climate system (atmosphere, oceans, ice sheets, etc), the most common measurement of global warming is taken by recording land and sea surface temperatures. Global surface temperatures fluctuate naturally year to year due to independent factors in the climate system, in particular a give-and-take exchange of heat with the oceans, a cyclical pattern that is superimposed upon on the long-term global warming trend. One of the most important fluctuations that affects global surface temperature is the El Niño Southern Oscillation (ENSO)—a natural fluctuation that transfers heat from deep in the ocean to the atmosphere during the El Niño phase, or that cools down the Earth's surface during the La Niña phase.
In 2014, the global average surface temperature set a new record without an assist from El Niño. The fact that 2014 set a new global temperature record in an ENSO-neutral year, besting the previous temperature record set only four years earlier in the El Niño year of 2010, reflects how warming due to human activity was enough to trump the natural year-to-year variation associated with the ENSO cycle. A study analyzing the contribution of El Niño and climate change to the global heat record of 2015 found that El Niño caused at most 10 percent of the warming, with the other 90 percent being due to climate change. In 2015, warming pushed the global average temperature past the record set in 2014 by the widest margin ever recorded.
In 2016, the record-strong El Niño of 2015-2016 boosted temperatures through mid-April 2016, but negative sea surface temperature anomalies persisted from July through December 2016. In October of 2016, the UK Met Office estimated that the 2015-2016 El Niño "only accounts for around 0.2°C [of the 0.86°C] global mean temperature rise in 2016 [as measured against the baseline of temperatures averaged between 1961 and 1990]. Increasing greenhouse gases are the main cause of warming since pre-industrial times." NASA researchers confirmed the estimate saying, "the direct impact of the natural El Niño warming in the tropical Pacific increased the annual global temperature anomaly for 2016 by 0.2°F (0.12°C) [of the observed 1.78°F (0.99°C) anomaly]."
This compares with a temperature rise of only 0.61°C in 2014, at the time a record breaking temperature rise reached during ENSO neutral conditions that year.
In addition to ENSO, other factors circulate heat through the climate system, helping to produce the classic staircase pattern in the warming of surface temperatures in which warming slows down and speeds up in alternating cycles.
One major factor that has been tentatively identified in driving this pattern on the decadal scale is the Pacific Decadal Oscillation, a circulation pattern that is often viewed as somewhat akin to ENSO but on a much longer time scale.
Independent global surface temperature analyses confirm 2016's record heat
There are four major global surface temperature datasets, kept by the National Oceanic and Atmospheric Administration (NOAA), the NASA Goddard Institute for Space Studies, the UK Met Office, and the Japanese Meteorological Agency (JMA). In addition, Berkeley Earth provides another widely used data set. These datasets record the most widely used proxy for global warming: land and sea surface temperatures. They are also considered the most accurate of the data sets, more accurate than satellite measurements (which measure temperatures throughout the troposphere). For more information on the differences between these records, see: "Why So Many Global Temperature Records?"
To reconstruct global temperatures, each agency divides the Earth’s surface into latitude-longitude grid boxes that are used to integrate temperature measurements from around the globe—including those from land-based weather stations and readings from ships and buoys that measure sea-surface temperature. The temperature at each land and ocean station is compared daily to what is ‘normal’ for that location and time, typically the long-term average over a 30-year period. The differences are called ‘anomalies’ and they help scientists evaluate how temperature is changing over time. Daily anomalies are averaged together over a whole month. These, in turn, are used to work out temperature anomalies from season-to-season and year-to-year. Global surface temperature anomaly data only records land and ocean temperature at the surface, and does not account for the vast amount of heat stored in the deep ocean.
Each of the four major global surface temperature datasets showed 2016 as the warmest year since record-keeping began in 1880:
- NOAA found that globally-averaged temperatures in 2016 were 1.69ºF (0.94ºC) above the 1901-2000 average
- NASA found that 2016 temperatures were 1.78°F (0.99°C) warmer than the mid-20th century mean
- The UK Met found 2016 was 1.38°F (0.77°C) above the long-term (1961-1990) average, nominally a record since at least 1850, and
- The Japan Meteorological Agency released a preliminary estimate on December 21, 2016 that finds the annual anomaly of the global average surface temperature for the year 2016 was 0.83°F (0.46°C) above the 1981-2010 average, likely to become the warmest record for the 126-year period since 1891. The JMA will release its final analysis in early February 2017.
According to NASA data, January, February, and March saw the highest departures from average of any month on record. The temperature anomaly for the month of February was 2.4°F (1.33°C) relative to a 1951-1980 baseline.
Satellite atmospheric temperature measurements also set new records in 2016
According to Remote Sensing Systems (RSS) analysis, 2016 was record warm by a large margin: 0.31°F (0.17°C) warmer than the previous record, set in 1998. The third warmest year occurred in 2010. In addition, 9 out of 12 months for 2016 were the warmest of that month ever recorded in the satellite record (excluding May, June, and December). "The record warmth was caused by long-term global warming combined with the strong El Niño event that occurred in the winter and spring of 2015-2016," according to the RSS press release.
University of Alabama in Huntsville (UAH) satellites also measured record warmth in 2016, which edged out 1998 by 0.036°F (0.02°C) to become the warmest year in UAH's 38-year satellite temperature record. Because the margin of error is about 0.10°C, this would technically be a statistical tie, with a higher probability that 2016 was warmer than 1998.
Satellite data is generally considered to be not as reliable as land and sea surface date for tracking climate change due to a number of technical issues including satellite drift and calibration for the frequent replacement of satellites.
There are five data sets based on satellite measurements of global average temperature in the troposphere (the part of the atmosphere where weather occurs). UAH provides two of them: TLT (temperature in the lower troposphere) and TMT (temperature in the mid-troposphere); while RSS provides three: TLT, TMT, and TTT (temperature in the total troposphere).
The long-term rate of warming is neither pausing nor accelerating, but is simply continuing, as predicted by climate models. However, the warming is essentially irreversible on human time-scales and will continue until all greenhouse gas emissions cease entirely. Analysis done by Dr. Jonathan Abraham in October of 2016 placed the predicted final global temperature for 2016 just above the average projection of computers models for that year.
The latest event has more or less put us back on track for what the models had suggested.
- Kevin Trenberth, NCAR
The planet’s average surface temperature has risen about 1.8°F (1°C) since the late-19th century, a change largely driven by increased carbon dioxide and other human-made emissions into the atmosphere.
Recent years, however, have been even warmer. The NOAA, NASA, UK Met, and JMA global surface temperature analyses use different, and relatively recent, baseline periods from which annual temperature deviations are determined. (NOAA compares annual temperatures relative to the 20th century average, 1901-2000; NASA uses 1951-1980; the UK Met uses 1961-1990; and the JMA uses 1971-2000.)
To calibrate NASA numbers against a baseline in the late 1800s (a common baseline used for calculating warming against the 1.5 and 2.0 degree limits set out in the UNFCCC Paris Agreement), former NASA climate center director Jim Hansen has calculated that an adjustment of +0.54°F (+0.3°C) should be made. With the adjustment, NASA data puts 2014 and 2015 at 1.9°F (1.05°C) and 2.1°F (1.16°C) above the pre-industrial average.
Andy Skuce, an independent geophysical consultant, adapts NASA's annual temperature anomaly data to a 1880-1909 baseline to illustrate the long-term trend.
He finds that the long-term trend is now above the 1.0°C anomaly level relative to pre-industrial temperatures and notes that the trend "shows remarkable linearity since 1980."
The difference between the long-term trend and accelerated warming in recent years represents the influence of El Niño and a resurgence of atmospheric warming after more than a decade of “slow" warming, when more of the heat went into the oceans.
Looking back at the last big El Niño, 1998, you will see another major and temporary spike in global temperature. If, however, you look at the long-term trend, 2016 is simply an extension of that trend.
Global warming is a staircase, not a straight upward line. Consistent with this pattern, the global average temperature for 2017 is expected to retreat and fall below the record set in 2016.
What 2016's record heat means for the 1.5°C warming limit
The long-term global average surface temperature trend, rather than annual records, is the best gauge for how close the global average temperature is to the ideal warming limit of 1.5°C (2.7°F) agreed upon in the Paris Climate Agreement.
Using his adapted analysis of NASA GISTEMP data, Skuce estimates that the 1.5°C threshold will be reached in about 25 years, by extending the trend line to 2050 (see chart in previous section).
However, the 1.5°C limit is now understood as a defense line, not a guard rail. Impacts are already accumulating and get worse as the global average temperature increases. The risk of passing tipping points also increases alongside temperature.
Already, with 1.8°F (1°C) of warming since the late 1800s, observations indicate that climate change is behind:
- 80 percent of new monthly extreme heat records globally
- 12 percent more record-breaking precipitation events globally over 1981–2010
- 55 percent of observed increases in aridity in Western US forests between 1979 and 2015, an important contributor to increased wildfire potential in recent decades
If greenhouse gas emissions continue to rise throughout the 21st century, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change projects that the global average temperature will rise 4.7°F to 8.6°F (2.6°C to 4.8°C) by 2081-2100 (relative to 1986-2005).
The higher end of this estimate puts temperatures in 2100 close to one of the planet's warmest periods in history known as the Paleocene-Eocene Thermal Maximum (PETM), which occurred about 55-56 million years ago. During the PETM, the global mean temperature appears to have risen by as much as 9-14°F (5-8°C) to an average temperature as high as 73°F. During this time the poles were free of ice caps, and palm trees and crocodiles lived above the Arctic Circle.
9°F (5°C) is the difference between the last Ice Age, when half of North America was covered in a mile-thick ice sheet, and today. Whereas that warming occurred over thousands of years, the Earth has warmed by 1.8°F (1°C) in just over 100 years. The projected rate of temperature change for this century is greater than that of any extended global warming period over the past 65 million years.
Notable heat records from the hottest year on record
Observed temperatures in Mitribah, Kuwait reached 129.2°F (54.0°C) on July 21st. This is the hottest temperature ever recorded in the Eastern hemisphere and possibly the hottest in the history of human measurement, since a 134°F degree temperature recorded in California’s Death Valley in 1913 is not universally accepted.
Thirteen countries broke their all-time temperature records in 2016, with temperatures in Kuwait, Iraq, India and Niger all rising past 120°F.
The Arctic experienced unprecedented heat in 2016. When 2016 began, the average temperature throughout the Arctic was fully 18°F (10°C) hotter than usual for New Year’s day. On March 24, 2016, sea ice in the Arctic hit 5.607 million mi² (14.52 million km²), its lowest annual maximum since records began in 1979. After summer sea ice extent dipped to its second-lowest on record, abnormally warm land and ocean temperatures slowed sea ice re-growth, leading 2016 to surpass the record year of 2012 for lowest sea ice extent on record in October through December. In mid-November, Arctic temperatures in the region above 80°N latitude reached 36°F (20°C) higher than normal.
New Zealand experienced its hottest year on record. The average temperature was 56.1°F (13.4°C), nearly 1°C warmer than usual (relative to a 1981-2010 baseline) and fractionally hotter than the previous record set in 1998.