2014 Was the Warmest Year Globally Ever Recorded

2014 had the highest global average temperature ever recorded.  The U. S. National Oceanic and Atmospheric Administration (NOAA)  and National Aeronautics and Space Administration (NASA ) jointly announced on Jan. 16, 2015 that the year 2014 was the hottest year since record keeping began in 1880.  This result represents the globally averaged temperature, for both land and ocean surfaces, over the entire year. 

A 1½ minute video from NASA gives more information on this finding.  It includes a speedy review, year-by-year and location-by-location across a map of the globe, of how annual average temperatures, in ºC (multiply by 1.8 for ºF), have increased from 1957 to 2014.  (They are shown as the differences from a 30-year reference period from about 1945 to about 1975).

The ten hottest years on record occurred between 1998 and the present (see Details section at the end of this post). 

[Update added January 26, 2015]: The United Kingdom Met (i.e., meteorological) Office jointly with the University of East Anglia reported, using their own data set, that 2014 was tied with 2010 as the being the warmest year on record, within the 95% confidence limit of their data.  This occurred even though 2014 did not experience a Pacific Ocean warming event known as El Nino.

The “pause” in rising temperatures of recent years is misleading. The new warm record for 2014 is significant because those who doubt the reality of global warming have pointed to an apparent “pause” in warming from about 1998 through 2013 (i.e., up to the time of the new NOAA/NASA report).  The apparent “pause” may be seen in the image below, compared to the clearly rising temperatures before 1998.

                 Global average temperature from 1980 to 2013.
                 Source: Data table from National Aeronautics and Space Administration;
                 http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.txt


The new result for 2014 places its data point slightly higher than the two next-warmest years, 2005 and 2010.  Although it is too early to tell, the new information suggests that the earth may be resuming its climb to higher global average atmospheric temperatures.

The “pause” is understood to be temporary, in any case, in view of the image below.

Global average temperatures from 1850 to 2012, presented as differences from the average temperature from 1961 to 1990.  The different colored lines represent different data records.  Top, annual data points; bottom, 10-year averages with the gray shading showing confidence estimates.

Source: Intergovernmental Panel on Climate Change, 5^th Assessment Report, Part 1; http://www.climatechange2013.org/images/uploads/WGIAR5-SPM_Approved27Sep2013.pdf

The graphic shows that there was an even longer “pause” between the late 1940’s and the mid 1970’s; nevertheless, that “pause” ended and the global average temperature rose dramatically in the three following decades.  Since trends in global warming become apparent only on long time scales, a decade or longer, the bottom panel in the graphic above, presenting atmospheric temperatures as ten-year averages, suggests that the purported “pause” in the first decade of the 21^st century may not be a significant “pause” at all.

Ocean Heat Content.  The temperatures discussed above relate only to surface air temperatures around the globe.  But 90% of the excess heat retained by the earth system is absorbed in the oceans, measured in an upper zone down to a depth of 700 m (2,296 ft), as well as in a deeper zone from the surface to 2,000 m (6,562 ft).  A graph showing the time dependence of the ocean heat content to both depths is seen in the image below.

Five-year averaged relative global ocean heat content through 2013 for the upper zone (0-700 m) and the full-depth zone (0-2000 m), evaluated as the difference from the average heat content between about 1975 and 1990. Source: NOAA; http://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/ .

Significantly, the image above shows clearly that during the present “pause” in the global average air temperature (1998-present) heat continued to accumulate in the waters of the oceans down to 2,000 m without any “pause”.  Thus, most of the excess heat absorbed by the earth system due to global warming is stored in the oceans.  Climate scientists have identified the role of the oceans in storing excess heat in recent publications, and pointed out that sooner or later that excess heat will be transferred back to the atmosphere (see Details, below).

Conclusions

The year 2014 had the hottest annual global average air temperature since record keeping began in 1880.  This result, and related information presented by NOAA and NASA, indicate  that there may be no significant “pause” in warming of the air temperature of the Earth, contrary to statements made by global warming skeptics and deniers.  The climate scientist Michael E. Mann, at the Pennsylvania State University, wrote  “It is exceptionally unlikely that we would be witnessing a record year of warmth, during a record-warm decade, during a several decades-long period of warmth that appears to be unrivaled for more than a thousand years, were it not for the rising levels of planet-warming gases produced by the burning of fossil fuels.”  Stefan Rahmstorf, head of earth system analysis at the Potsdam (Germany) Institute for Climate Impact Research stated   “[T]he fact that the warmest years on record are 2014, 2010 and 2005 clearly indicates that global warming has not ‘stopped in 1998,’ as some like to falsely claim.”

Indeed, 90% of the excess heat retained by the earth system is absorbed by the oceans, a process continuing without a “pause” up to the present.  Long-lived ocean currents redistribute this heat around the earth and among zones of varying depth.  It takes many years for heat to re-emerge to the surface and exchange back into the atmosphere.  Yet it is considered essentially certain that this will indeed occur. 

Global warming due to continued emissions of greenhouse gases will continue indefinitely unless greenhouse gas emissions are reduced.  If the peoples of the earth succeed in lowering annual emission rates to near zero, further warming will come to an end, and the earth will experience a new, higher global average temperature than we have now.  We must strive to reduce annual emission rates to (near) zero in order to minimize the additional warming of the earth.

Details

The ten hottest years on record occurred between 1998 and the present.  The second hottest years, only slightly less warm on average than 2014, were 2005 and 2010 (see the first graphic above).   The finding that 2014 exceeded all other records is even more significant because it occurred in a year in which the El Nino Southern Oscillation, a warming pattern in the Pacific Ocean, was absent. 

NOAA presents the global map, below, showing deviations in temperature from the reference period 1981-2010 as color-coded shades grading the deviations from the average.

Global grid showing color-coded deviations of the temperature in 2014 from the average temperature over the period 1981-2010.  Red shades represent temperatures warmer than the average, and blue shades represent temperatures cooler than the average.  (Grey regions had no data available.)

Source: NOAA; http://www.ncdc.noaa.gov/sotc/global/2014/13

  

The image above is noteworthy, since it shows that there were many regions, both on land and oceanic, recording record warmest average temperatures whereas there was only one region, south of South America, having a record coldest average temperature.  Indeed, most regions of the earth, both land and sea, had temperatures in 2014 higher than the 1981-2010 average.
 

Climate scientists have pointed out in recent publications that heat is accumulating in the oceans and that sooner or later the excess heat will re-emerge, so that the global average air temperature will resume climbing.

Loeb and coworkers (Nature Geoscience, vol. 5, pp. 110–113 (2012) doi:10.1038/ngeo1375) compared the energy imbalance of the Earth system with ocean heat content.   Combining satellite temperature measurements and ocean heat measurements to 1,800 m (5,900 ft) they found “between January 2001 and December 2010, Earth has been steadily accumulating energy at a [significant rate]. We conclude that energy storage is continuing to increase in the sub-surface ocean.”

Guemas and coworkers (Nature Climate Change vol. 3, pp. 649–653 (2013) doi:10.1038/nclimate1863)  examined the current “pause” in global warming.  Using historical ocean temperature data and a coupled ocean-atmosphere climate model, they “attribute the onset of [the “pause”] to an increase in ocean heat uptake.”  They verify that no reduction in the sun’s radiation was found which could explain the “pause”.

Chen and Tung (Science Vol. 345, pp. 897-903 (2014)  DOI: 10.1126/science.1254937) analyzed earlier data as well as more extensive newer observations gathered by buoys disposed worldwide at various ocean depths.  They found that “the [“pause”] is mainly caused by heat transported to deeper layers in the Atlantic and the Southern oceans….Cooling periods associated with the latter deeper heat-sequestration mechanism historically lasted 20 to 35 years.”  They further conclude “because the planetary heat [reservoirs] in the Atlantic and the Southern Oceans remain intact, the [“pause”] should continue on a decadal time scale. When the internal variability that is responsible for the current [“pause”] switches sign, as it inevitably will, another episode of accelerated global warming should ensue.”

© 2015 Henry Auer

Deniers Mistakenly Say that Global Warming Has Ended

Global Average Temperatures and CO₂.  The global average temperature has increased by about 0.7-0.8ºC (1.3-1.4ºF) over pre-industrial values.  Humanity’s use of fossil fuels to power industrialization emits carbon dioxide (CO₂), a greenhouse gas, leading to warmer average temperatures.  Analysis of the increased CO₂ levels shows that they arise directly from burning fossil fuels, and not from natural causes (see also the U. S. National Climate Assessment).

Climate deniers do not accept that our planet is warming, and/or that human activity is its cause.  Climate skeptics may question that human actions are responsible for warming, or that warming is harmful to human populations and other life forms.  Here both groups will be called “deniers”.

Climate deniers claim that global warming has ended.  They selectively display global temperature data for, say, the period 1980 to the present, as shown in this graphic:

 

 

Yearly values of the global average temperature selected for the interval 1980-2013, shown as their difference from the average temperature for the entire 20^th century.

Source: Data table from National Aeronautics and Space Administration;

http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.txt.

 

 

Other more biased presenters don’t show any data before 1997.  These deniers point to the interval after 1997 as showing that the temperature has remained essentially unchanged (here called the “pause”), breaking with the upward trend from 1980 to 1997.  Since atmospheric CO₂ concentrations continued to increase during the pause period (see below), deniers state that increasing atmospheric concentrations of CO₂ cannot be the cause for global warming.

 

Deniers  cannot selectively choose the data they wish to use while rejecting the entire data set from consideration.  It is unacceptable to focus arbitrarily on only the period supporting their view while ignoring the extended global temperature record.  Data covering most of the industrial era, 1880-present, are shown below. 

 

Yearly values of the global average temperature for 1880-2013, shown as the differences from the average temperature for the entire 20^th century.  Black points and line, annual average temperature differences; Red line, smoothing obtained as a 5-year running window centered at each data point; Green, error bars showing estimates of uncertainty in the measurements.

Source: National Aeronautics and Space Administration.  http://data.giss.nasa.gov/gistemp/graphs_v3/

 

 

The overall trend shows a clear, if uneven, rise in the global average temperature beginning at about 1910, coinciding with increasing atmospheric levels of CO₂ (see below and this post).  Importantly, a seemingly long pause also occurred from about 1950-1975, followed by more than 20 years in which the temperature rose sharply.  It is noteworthy that deniers fail to mention this earlier pause as evidence that warming has ceased.

 

A Simple Inert Earth Model.  Deniers are incorrectly assuming that in the Earth system, the only factor affecting the air temperature around the globe is the amount of CO₂ in the atmosphere.  Such a simple model, featuring an inert Earth, may be illustrated using the following graphic.  

Model for a simplified inert Earth system close to radiation balance.  It re-emits much of the sun’s energy back into space as heat (infrared) radiation.  In this model only the atmosphere retains excess heat.  © Henry Auer

 

In essence, deniers ignore any additional components in the Earth system that affect the energy balance.

A Complex Earth System Model.  Why is the Earth’s temperature record so erratic?  Why do these pauses occur?  The answer to these questions is that the Earth is not a simple object inert to the effects of the sun’s energy.  Rather, the Earth is a complex system that responds to inputs of excess energy from the sun in many ways.  This can be modeled by a complex Earth system in the image below.

Model of the Earth system, including CO₂ in its atmosphere and potential reservoirs of heat in the land, the oceans and the polar ice caps.  This Earth is not in energy equilibrium; less energy is radiated back into space than the energy falling on it from sunlight.  The extra energy heats the entire earth system, with most of the heat being stored in the ocean rather than in the atmosphere. © Henry Auer

 

This more realistic model for Earth is not in energy balance.  Direct satellite measurements of radiation leaving Earth are compared with sunlight energy reaching the Earth.  Because of the greenhouse effect the Earth retains excess heat, rather than re-emitting it back into space.  

Most of the retained heat is stored in the oceans, and not in the atmosphere.  This is why deniers are mistaken by speaking in terms of an inert Earth model, i.e., in assuming that the temperature in the atmosphere is determined only by the atmospheric CO₂ concentration.  This is shown in the following graphic.

 

Top panel: Total heat energy stored in the top half-mile of Earth’s oceans compared to the average from 1955-2006.  Middle panel: Yearly global average temperature compared to the average value for the full 20^th century (repeating the pattern shown in the earlier graphic).  Bottom panel: Direct measurement of atmospheric CO₂ from 1958 in parts per million (ppm).

Source: National Oceanic and Atmospheric Administration;

http://www.climate.gov/maps-data.

 

 

It is seen from the lower panel that the CO₂ concentration has been rising steadily since 1958; indeed a smooth curve such as seen here extends back to pre-industrial times, when the concentration was 280 ppm.  The pronounced variability in the temperature data (middle panel) contrasts with the smooth, steady increasing trend seen  for CO₂.  This suggests, as indicated above, that factors other than only the atmospheric CO₂ concentration are at play. 

 

90% of the excess heat retained in the Earth system is stored in the oceans.  The data in the top panel show that heat energy absorbed by the oceans has been steadily increasing since at least about 1970, including the prior pause of global atmospheric temperature, and has continued to increase even during the current pause.  Instead of ending up warming the atmosphere, excess heat has been absorbed into the oceans, warming them (see the Details section at the end of this post).  Since oceans have decade-long cycles of vertical as well as lateral currents, this heat remains latent in the oceans, but will eventually be transferred back to the atmosphere, renewing the trend of increasing global atmospheric temperature.  

 

Conclusion

 

The long-term global average temperature has increased by about 0.7-0.8ºC over pre-industrial temperatures.  A current pause of annual global temperatures began after 1997 even though the atmospheric concentration of CO₂ continued to increase during this period.  Global warming deniers have seized on this pause to say that warming of the Earth has ended, since the air temperature has not responded to the increased CO₂ concentration on a year-by-year basis. 

 

In fact direct measurements of the Earth’s energy balance show that it does retain excess heat, but does not store it in the atmosphere.  Rather, the excess heat enters the oceans.  It is stored there as deep as 1,500 m (4,920 ft) in slow-moving ocean currents, both lateral and vertical.  As the warmer water is lifted to the surface again, it will exchange this stored heat with the atmosphere, resuming the warming of the air.  Similar processes happened in an earlier pause event.  Global (atmospheric) warming continues on the extended time scales dictated by Earth system processes.  Global warming deniers are mistaken in saying that global warming has ended.

 

Details

 

Guemas and coworkers (Nature Climate Change vol. 3, pp. 649–653 (2013); doi:10.1038/nclimate1863)  examined the current pause in global warming.  They used earlier data as a baseline to project sea surface temperatures forward up to 2010 using a coupled ocean-atmosphere climate model.  From their results they “attribute the onset of [the pause] to an increase in ocean heat uptake.”  They verify that no reduction in the sun’s radiation can explain the pause.

 

Loeb and coworkers (Nature Geoscience, vol. 5, pp. 110–113 (2012); doi:10.1038/ngeo1375) compared the energy imbalance of the Earth system with ocean heat content.  They measured radiated heat energy and sea temperatures.  They found that the energy imbalance of the Earth system and the increase in the upper-ocean heat content are similar in magnitude.  Combining satellite temperature measurements and ocean heat measurements to 1,800 m (5,900 ft) they found “between January 2001 and December 2010, Earth has been steadily accumulating energy at a [significant rate]. We conclude that energy storage is continuing to increase in the sub-surface ocean.”

 

Chen and Tung (Science Vol. 345, pp. 897-903 (2014)  DOI: 10.1126/science.1254937) analyzed earlier data as well as more extensive newer observations gathered by buoys disposed worldwide at various ocean depths.  They found that “the [pause] is mainly caused by heat transported to deeper layers in the Atlantic and the Southern oceans….Cooling periods associated with the latter deeper heat-sequestration mechanism historically lasted 20 to 35 years.”  They further conclude “because the planetary heat [reservoirs] in the Atlantic and the Southern Oceans remain intact, the [pause] should continue on a decadal time scale. When the internal variability that is responsible for the current [pause] switches sign, as it inevitably will, another episode of accelerated global warming should ensue.”

 

© 2014 Henry Auer