September 2018 Global Temperature Update

September 2018 Global Temperature Update

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September 2018 global temperature, at 0.75°C relative to the 1951-1980 base period, was the sixth warmest September (tied with 2005) since reliable measurements began in 1880, with some very warm and very cold areas in the northern high latitudes (left side of the figure on the top).  Most of Europe and the U.S. were 1-3°C warmer than the 1951-1980 mean.  Warmer Septembers occurred in 2014 and 2016 (+0.88°C), 2015 (+0.82°C), 2013 (+0.77°C) and 2017 (+0.76°C).  January through September means were, from the warmest, 2016 (1.03°C), 2017 (0.91°C), 2018 (0.81°C) and 2015 (0.80°C).  2018 seems likely to end up as the fourth warmest year since 1880.

For the base period 1880-1920, which provides our best estimate of pre-industrial temperature, the September 2018 anomaly was 1.02°C.  Models predict an El Nino to begin in the next few months, and the tropical Pacific has begun to warm.  We conclude that global temperature has reached a level of at least 1°C relative to pre-industrial climate even in the presence of La Nina cooling.

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Global Warming and East Coast Hurricanes

Global Warming and East Coast Hurricanes

17 September 2018

James Hansen and Makiko Sato

This Communication is also our Monthly Temperature Update for August 2018. Monthly temperature updates are available from either web page (Hansen or Sato) or directly here.

Maps below show the temperature anomaly for the past three months and the seasonal mean (Northern Hemisphere Summer). We draw attention to the cool region southeast of Greenland and warmth in the middle of the North Atlantic.

Wally Broecker suggested decades ago that freshwater injection onto the North Atlantic could cause shutdown of the overturning ocean circulation (AMOC, Atlantic Meridional Overturning Circulation). Rahmstorf et al. (2015)[1] present evidence that a 20th century trend toward the cooling southeast of Greenland was due to a slowdown of AMOC, linking the trend to observed freshening of the North Atlantic surface water that may have been due to some combination of anomalous sea ice export from the Arctic, Greenland melt, and increased precipitation and river runoff.

In our paper on ice melt, sea level rise and superstorms[2] we conclude from multiple lines of evidence that a 21st century slowdown of AMOC is underway. Ocean surface temperature response to AMOC slowdown, in addition to cooling southeast of Greenland, includes warming off the U.S. East Coast, a temperature pattern emerging from high ocean resolution simulations (Saba et al., 2015)[3] .

So, does global warming have a hand in the magnitude of the Hurricane Florence disaster on the U.S. East Coast? Yes, we can say with confidence, it contributes in several ways.

First, there is the fact that sea level rise due to global warming is already well over a foot along the U.S. East Coast. Ice melt due to global warming accounts for about 20 cm (8 inches) global average sea level rise (Fig. 29 in our Ice Melt paper[2]). Slowdown of the Gulf Stream, which is a part of the AMOC slowdown, adds to East Coast sea level. The slowdown reduces the west-to-east upward slope of the ocean surface across the Gulf Stream[4] , causing piling up of water on the East Coast. The combined sea level rise from these effects, which is also responsible for “sunny day flooding” on the Eastern Seaboard, makes hurricane storm surges greater.

 Figure 1. Surface temperature anomalies for the past three months.

Figure 1. Surface temperature anomalies for the past three months.

Second, the warmer ocean surface and atmosphere result in greater rainfall amounts. Of course the primary reason for extraordinary rainfall amounts from Florence was the storm’s slow movement.

Third, warmer ocean surface provides more fuel for tropical storms and expands the ocean area able to generate and maintain these storms. Part of a given hurricane’s strength can be attributed to such extra warming of the ocean surface. That effect was pronounced in the case of Hurricane Sandy, which maintained hurricane wind speeds all the way to New York City because of the unusually warm sea surface off the United States East Coast.

What about the track of Florence and the fact that it stalled, resulting in huge local rainfall totals? The track and speed of a given hurricane depend on large scale mid-latitude weather patterns that are largely a matter of chance. As the area in which “tropical” storms can form expands poleward, the opportunity for a mid-latitude high pressure system to push a storm westward may increase, but we are unaware of specific studies. What we can say is that historical hurricane tracks may not be an accurate picture of future tracks.

The number of hurricanes striking the continental U.S. does not show a notable trend (Fig. 2). Indeed, the current decade has only the rest of this year and next year to add to its total to avoid being the decade with the smallest number of hurricanes hitting the continental United States. This small reduction in landfalls seems to be a matter of chance[5]. Damage per hurricane is more important. Global warming already has a large impact on damage for reasons given above. Those impacts, especially those arising from increasing sea level, may accelerate exponentially, if high fossil fuel emissions continue[2].

 Fig. 2. The three category 5 hurricanes to strike the U.S. were: Labor Day (Sept. 1935, SW FL, 892 hPa, 184 mph), Camille (Aug 1969, LA & MS, 909 hPa), Andrew (Aug 1992, SE FL, 922 hPa, 167 mph); source: http://www.aoml.noaa.gov/hrd/hurdat/All_U.S._Hurricanes.html.

Fig. 2. The three category 5 hurricanes to strike the U.S. were: Labor Day (Sept. 1935, SW FL, 892 hPa, 184 mph), Camille (Aug 1969, LA & MS, 909 hPa), Andrew (Aug 1992, SE FL, 922 hPa, 167 mph); source: http://www.aoml.noaa.gov/hrd/hurdat/All_U.S._Hurricanes.html.

 

[1] Rahmstorf, S., J. E. Box, G. Feulner, M.E. Mann, A. Robinson, S. Rutherford, and E.J. Schaffernicht: Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Clim. Change, 23 March 2015, 10.1038/nclimate2554.

[2] Hansen, J., M. Sato, P. Hearty, R. Ruedy, M. Kelley, V. Masson-Delmotte, G. Russell, G. Tselioudis, J. Cao, E. Rignot, I. Velicogna, B. Tormey, B. Donovan, E. Kandiano, K. von Schuckemann, P. Kharecha, A.N. Legrande, M. Bauer, and K.-W. Lo: Ice melt, sea level rise and superstorms:/ evidence from paleoclimate data, climate modeling, and modern observations that 2 C global warming could be dangerous Atmos. Chem. Phys., 16, 3761-3812. doi:10.5194/acp-16-3761-2016.

[3] Saba, V.S., Griffies, S.M., Anderson, W.G., Winton, M., Alexander, M.A., Delworth, T.L., Hare, J.A., Harrison, M.J., Rosati, A., Vecchi, G.A., and Zhang, R.: Enhanced warming of the Northwest Atlantic Ocean under climate change, J. Geophys. Res., 120, doi:10.1002/2015JC011346, 2015.

[4] Ezeer, T. and L. P. Atkinson: Accelerated flooding along the U.S. East Coast: On the impact of sea-level rise, tides, storms, the Gulf Stream, and the North Atlantic Oscillations, Earth’s Future, 2, 362-382, 2014.

[5] Hall, T. and E. Yonekura: North American tropical cyclone landfall and SST: a statistical model study, J. Climate, 26, 8422- 8439, 2013.

July 2018 Global Temperature Update

July 2018 Global Temperature Update

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Heat waves seemed unusually widespread in July, as the media reported extreme heat in Europe, the Middle East, northern Africa, Japan and western United States.  Extreme heat contributed to extensive wildfires in the western United States, Greece and Sweden, with fire extending into the Arctic Circle.  

The left map is the global distribution of temperature anomalies with our usual 1200 km smoothing; the right map has 250 km smoothing and uses only meteorological stations (no sea surface temperatures).   Area-weighted warming over land (1.14°C) is 1.5 times larger than global warming (0.78°C), consistent with data for the past century (see graphs at http://www.columbia.edu/~mhs119/Temperature/T_moreFigs/).

Globally July 2018 was the third warmest July since reliable measurements began in 1880, 0.78°C warmer than the 1951-1980 mean.  The warmest Julys, in 2016 and 2017, were 0.82°C and 0.81°C, respectively.  July 2018 temperature was +1.06°C relative to the 1880-1920 base period, where the latter provides our best estimate of pre-industrial global temperature.

It is incorrect to describe the July 2018 climate conditions in the global hotspots as a “new normal” climate for those regions.  Hotspots move from one summer to another.  Sweden, for example, may have a much cooler summer next year.  However, the chance of having such extreme conditions is increasing dramatically.  Realistic description of the changing climate is perhaps shown best by our shifting “bell curves” for seasonal temperature anomalies (Regional Climate Change and National Responsibilities).

Figure 2, from our paper, shows that global warming has greatly increased the frequency or chance of an extreme hot summer, e.g., two standard deviations or more warmer than average 1951-1980 climate.  The bell curve is shifted by 1-1.5 standard deviations by 2005-2015 in the regions shown in Figure 2.

An important point is that the bell curves are continuing to shift, which is another reason not to suggest a fixed “new normal.”  How much has the bell curve continued to shift in just the past few years?

The 2015-2018 global temperature relative to 1951-1980 is +0.90, which compares with +0.66 for the period 2005-2015.  To a good approximation an increase of global warming from +0.66 to +0.90°C increases the rightward shift of the bell curve shown for 2005-2015 by the factor 0.90/0.66 ~ 1.36.

  Figure 2.  Bell curves that define the frequency of local temperature anomalies relative to 1951-1980 base period.  Numbers above maps are % of globe covered by the selected region.  ‘Shift’ and ‘width’ refer to 2005-2015 data.

Figure 2. Bell curves that define the frequency of local temperature anomalies relative to 1951-1980 base period.  Numbers above maps are % of globe covered by the selected region.  ‘Shift’ and ‘width’ refer to 2005-2015 data.

This large warming and movement of the bell curve, if it is representative of the coming decade, is an acceleration of the warming trend.  Of course, a strong El Nino (Figure 3) contributed to 2015-2018 warmth.  However, we will argue that the present 12-month running mean (Fig. 3) has already reached the inter-El Nino minimum global temperature, at a value that is above the trend line for the average.

If the latter assertion is correct, we may have entered a period of accelerated global warming.  Jeremy Grantham, in The Race of Our Lives Revisited, draws that conclusion from comparison of global temperatures at the peaks of the last two El Ninos.  An acceleration of warming is consistent with recent acceleration of climate forcings described in Young people's burden: requirement of negative CO2 emissions.  We will take a closer look at acceleration of global warming in our next Communication

  Figure 3.   Global surface temperature relative to 1880-1920 based on GISTEMP analysis (Hansen, J., Ruedy, R., Sato, M., and Lo, K.:   Global surface temperature change , Rev. Geophys., 48, RG4004, 2010.).

Figure 3.  Global surface temperature relative to 1880-1920 based on GISTEMP analysis (Hansen, J., Ruedy, R., Sato, M., and Lo, K.:  Global surface temperature change, Rev. Geophys., 48, RG4004, 2010.).

Climate shifts in the subtropics in the summer and in the tropics all year, as shown if Figure 4, are larger than at higher latitudes, with the unit of measurement being the standard deviation of local temperature.  Warming in these regions is particularly important, because the regions were already hot without added warming.  There is a danger that these regions will become less livable, increasing the pressures for migration, as discussed in Regional Climate Change and National Responsibilities.

  Figure 4.   Bell curves that define the frequency of local temperature anomalies relative to 1951-1980 base period.  Numbers above maps are % of globe covered by the selected region.  ‘Shift’ and ‘width’ refer to 2005-2015 data.

Figure 4.  Bell curves that define the frequency of local temperature anomalies relative to 1951-1980 base period.  Numbers above maps are % of globe covered by the selected region.  ‘Shift’ and ‘width’ refer to 2005-2015 data.


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June 2018 Global Temperature Update

June 2018 Global Temperature Update

june temp fig1.png

Globally June 2018 was the third warmest June since reliable measurements began in 1880, 0.77°C warmer than the 1951-1980 mean. June 2018 temperature was +1.07°C relative to the 1880-1920 base period, which provides our best estimate of pre-industrial global temperature. 2015 and 2016 June anomalies were 0.80°C and 0.79°C, respectively, and 1998 tied with 2018 at 0.77°C.

The left side of the figure above shows the global distribution of June 2018 temperature, and the right side compares temperatures in the years 2015-2018 month by month. Note that temperature began rising in the latter part of 2015 as an El Nino was developing. That late 2015 warming led to record 2016 global heat. Some ocean models predict that an El Nino may develop later this year, in which case 2019 could be a very hot year. Historical precedence does not favor the occurrence of two strong El Ninos separated by only 3 years. On the other hand, the human hand may be altering history.

January-June this year was the 3rd warmest on record as shown below.

june temp fig2.png

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May 2018 Global Temperature Update

May 2018 Global Temperature Update

may 2018 global temp fig1.png

May 2018 global temperature, at 0.82°C relative to the 1951-1980 base period, was the fourth warmest May since reliable measurements began in 1880.  The warmer Mays were in 2016 (+0.91°C), 2017 (+0.88°C) and 2014 (+0.85°C).  Northern Hemisphere spring (March-April-May) 2018 was the third warmest spring at 0.86°C (See the figure above), while the warmest were 2016 (1.10°C) and 2017 (0.97°C).  Note that the most of the U.S. was extremely cold in April and very warm in May.

Using the base period 1880-1920 which provides our best estimate of pre-industrial temperature, the May 2018 anomaly was 1.09°C.  Post-El Nino cooling has probably bottomed out, given that equatorial Pacific Ocean temperatures have begun to rise (See the left side of the figure below).  We conclude that global warming, with short-term variability excluded, has reached the level of at least +1.1°C relative to pre-industrial temperature.

may 2018 global temp fig2.png

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APRIL 2018 GLOBAL TEMPERATURE UPDATE

APRIL 2018 GLOBAL TEMPERATURE UPDATE

April 2018 Global Temp Update figure.png

Two-thirds of North America was very cold in April (left side of figure above), but globally April 2018, at 0.86°C relative to the 1951-1980 base period, was the third warmest April since reliable measurements began in 1880.  The warmest Aprils were in 2016 (+1.07) and 2017 (+0.92°C)!

The right side of the figure above compares monthly temperatures in the years 2015-2018. 

Post-El Nino cooling has probably bottomed out, given that equatorial Pacific Ocean temperatures have begun to rise.  We conclude that global warming, with short-term variability excluded, has reached the level +1.1°C relative to pre-industrial temperature, as shown in the figure below.

Note that base period 1880-1920, used for the figure below, provides our best estimate of pre-industrial temperature, as discussed in our Young People’s Burden paper (Earth System Dyn., 8, 1-40, 2017).

Also note that the reason we employ base period 1951-1980 in the figure above is the absence of earlier data for Antarctica, much of the Southern Ocean, and parts of Africa and South America.  There are enough data points to define a global mean temperature, but not to define a global map.

April 2018 Global Temp Update figure2.png

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March 2018 Global Temperature Update

March 2018 Global Temperature Update

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Globally March 2018 was the sixth warmest March since reliable measurements began in 1880, 0.89°C warmer than the 1951-1980 mean.  March temperature was +1.16°C relative to the 1880-1920 base period that provides our best estimate of pre-industrial global temperature.  March temperatures relative to 1951-1980 mean, in order from the warmest, were +1.30°C (2016), +1.12°C (2017), +0.92°C (2010), +0.91°C (2002) and +0.90°C (2015).

The figure above compares monthly temperatures in the years 2015-2018.  Note that temperature began rising in the latter part of 2015 as an El Nino was developing.  That late 2015 warming led to record 2016 global heat.  Some ocean models predict that an El Nino may develop later this year, in which case 2019 could be a very hot year.  Historical precedence does not favor the occurrence of two strong El Ninos separated by only 3 years.  On the other hand, the human hand may be altering history.

January-March this year was the 4th warmest on record, but the maps below for the geographical distribution of the temperature anomaly confirm that Europe and the U.S. were not particularly warm.  However, it was nothing like the extreme 2015 cold period in the eastern part of Canada and the U.S., which caused some of the public to doubt the reality of global warming.

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February 2018 Global Temperature Update

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Additional figures are on our global temperature web page.

Globally February 2018 was the sixth warmest February since reliable measurements began in 1880, 0.78°C warmer than the 1951-1980 mean.  February temperature was +1.06°C relative to the 1880-1920 base period that provides our best estimate of pre-industrial global temperature.  February temperatures relative to 1951-1980 mean, in order from the warmest, were +1.34°C (2016), +1.12°C (2017), +0.90°C (1998), +0.87°C (2015) and +0.79°C (2010).  A comparison of the monthly mean temperatures for 2015-2018 is shown in the figure above.

febtemp2018.png

As one of the maps above shows, February was cold in Western Europe and Japan, but a large region from Canada to the northern central US was 4-6°C colder than the 1951-1980 mean, while the Arctic region was 8-12°C warmer than normal.  Such cold air outbreaks from the Arctic to middle latitudes, with accompanying movement of warm mid-latitude air into the Arctic, have always occurred because of natural variability of atmospheric wind patterns.  However, there is evidence (Cohen et al., 2018) that the frequency of winter cold air outbreaks from the Arctic has increased as a result of global warming.  Average warming is greater in the Arctic than at lower latitudes, in part because global warming reduces the area of Arctic sea ice, which amplifies the polar warming.  The greater polar warming reduces the temperature gradient between low and high latitudes that drives the mid-latitude jet stream, the west-to-east wind in the upper troposphere.  A weaker jet stream tends to be more “waggly,” increasing the occurrence of Arctic cold air outbreaks.

The situation is different in the Antarctic.  The surface of the Southern Ocean is warming more slowly than most of the planet, in part because of the cooling and freshening effects of increasing ice discharge from Antarctic ice shelves (Hansen et al., 2016).  This cooling effect on the surface of the Southern Ocean competes regionally with the warming effect of increasing greenhouse gases.  There is large year-to-year variability; the strong 2016-17 El Nino caused a decrease of Southern Ocean sea ice over the past two years.  However, if melting of Antarctic ice shelves and ice sheets continues to increase, the warming of the Southern Ocean will continue to be much less than warming in the rest of the world.

Cohen, J., K. Pfeiffer and J.A. Francis, Warm Arctic episodes linked with increased frequency of extreme weather in the United States, Nature Comm., publ. online 13 March 2018.

Hansen, J., M. Sato, P. Hearrty, R. Ruedy, M. Kelley, V. Masson-Delmotte, G. Russell, G. Tselioudis, J. Cao, E. Rignot, I. Velicogna, B. Tormey, B. Donovan, E. Kandiano, K. von Schuckmann, P. Kharecha, A.N. Legrande, M. Bauer, and K. Lo, Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2°C global warming could be dangerous, Atmos. Chen. Phys., 16, 1-52, 2016.

January 2018 Global Temperature Update

January 2018 Global Temperature Update

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Globally January 2018 was the fifth warmest January since reliable measurements began in 1880, 0.78°C warmer than the 1951-1980 mean. January temperature was +1.05°C relative to the 1880-1920 base period that provides our best estimate of pre-industrial global temperature. January temperatures relative to 1951-1980 mean, in order from the warmest, were +1.16°C (2016), +0.97°C (2017), +0.95°C (2007) and +0.81°C (2015).

The strong 2015-2016 El Nino ended about a year and half ago and the tropical Pacific is now in a La Nina phase (temperature anomaly less than -0.5°C; see left side of above figure). Because this year is starting in a deep La Nina, 2018 is likely to decline further relative to the past year, but note that 2017 was still 0.1C above the global warming trend line
(http://www.columbia.edu/~jeh1/mailings/2018/20180118_Temperature2017.pdf). Some ocean models are projecting a possible El Nino in the latter part of 2018, which would tend to reverse the recent short-term cooling trend.

The geographical distributions of January temperature for the past four years are shown below.

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Global Temperature in 2017

Global Temperature in 2017

18 January 2018

James Hansen[a], Makiko Sato[a], Reto Ruedy[b,c], Gavin A. Schmidt[c], Ken Lo[b,c], Avi Persin[b,c]

 

Abstract.  Global surface temperature in 2017 was the second highest in the period of instrumental measurements in the Goddard Institute for Space Studies (GISS) analysis.  Relative to average temperature for 1880-1920, which we take as an appropriate estimate of “pre-industrial” temperature, 2017 was +1.17°C (~2.1°F) warmer than in the 1880-1920 base period.  The high 2017 temperature, unlike the record 2016 temperature, was obtained without any boost from tropical El Niño warming.

Update of the GISS (Goddard Institute for Space Studies) global temperature analysis (GISTEMP)[1],[2](Fig. 1), finds 2017 to be the second warmest year in the instrumental record.  (More detail is available at http://data.giss.nasa.gov/gistemp/ and http://www.columbia.edu/~mhs119/Temperature; figures here are available from Makiko Sato on the latter web site.)  A few figures are included below as an appendix.

We take 1880-1920 as baseline, i.e., as the zero-point for temperature anomalies, because it is the earliest period with substantial global coverage of instrumental measurements and because it also has a global mean temperature that should approximate “preindustrial” temperature[3].

      We estimate current underlying temperature, excluding short-term variability via linear fit to the post-1970 temperature (Fig. 1).  The result is +1.07°C at the beginning of 2018 relative to 1880-1920.

      Figure 2 compares maps of global temperature anomalies of the past three years.  The map in the lower right is the difference between 2017 and 2015 temperatures, revealing that 2017 was notably warmer than 2015 in the polar regions.  This 2017-2015 difference map suggests the reason why some temperature analyses report 2017 as the third warmest year, behind 2015 as well as 2016.  Some analyses include only area close to the points of actual observations in their ‘global’ analysis.  The GISS analysis[1] extrapolates observations as far as 1200 km from measurement points, thus covering practically the entire globe.  It has been shown, by sampling globally complete data with realistic temporal and spatial variability, that this extrapolation procedure yields a more accurate estimate of annual global temperature than global integration methods that restrict the area to regions very close to observed points.[4],[1]

   Fig. 1.    (a) Global surface temperatures relative to 1880-1920 based on GISTEMP data, which employs GHCN.v3 for meteorological stations, NOAA ERSST.v5 for sea surface temperature, and Antarctic research station data[1].

Fig. 1. (a) Global surface temperatures relative to 1880-1920 based on GISTEMP data, which employs GHCN.v3 for meteorological stations, NOAA ERSST.v5 for sea surface temperature, and Antarctic research station data[1].

   Fig. 2.    Temperature anomalies in 2017, 2016 and 2015 relative to 1951-1980 base period.  The lower right map shows the difference between the 2017 and 2015 maps.  We use the 1951-1980 base period for maps because of more limited global data coverage in 1880-1920.

Fig. 2. Temperature anomalies in 2017, 2016 and 2015 relative to 1951-1980 base period.  The lower right map shows the difference between the 2017 and 2015 maps.  We use the 1951-1980 base period for maps because of more limited global data coverage in 1880-1920.

Figure 3 compares the GISS analysis of global temperature change with the case in which the polar regions, specifically regions poleward of 64 degrees latitude, are excluded from the analysis.  With polar regions excluded, 2017 becomes the third warmest year, and the ‘global’ warming relative to the base period is reduced by almost a tenth of a degree Celsius.  We do not mean to imply that other analyses entirely exclude polar regions.  Therefore we make a more specific test of the impact of omitted regions by carrying out the GISS analysis with local measurements extrapolated only 250 km rather than 1200 km.  Fig. A2 shows that this area limit also causes 2017 to be only the third warmest year.

      We conclude that 2017 probably was the second warmest year.  However, the temperatures of 2015 and 2017 are so close that the difference is unimportant.

      Prospects for continued global temperature change are more interesting and important.  The record 2016 temperature was abetted by the effects of both a strong El Niño and maximum warming from the solar irradiance cycle (Fig. 4).  Because of the ocean thermal inertia and decadal irradiance change, the peak warming and cooling effects of solar maximum and minimum are delayed about two years after irradiance extrema.  The amplitude of the solar irradiance variation is smaller than the planetary energy

   Fig. 3.    Global temperature compared with the result for integration over the region from 64°N to 64°S, which covers 90% of Earth’s surface, excluding only polar regions.

Fig. 3. Global temperature compared with the result for integration over the region from 64°N to 64°S, which covers 90% of Earth’s surface, excluding only polar regions.

  Fig. 4.   Solar irradiance and sunspot number in the era of satellite data.  Left scale is the energy passing through an area perpendicular to Sun-Earth line.  Averaged over Earth’s surface the absorbed solar energy is ~240 W/m2, so the full amplitude of the measured solar variability is ~0.25 W/m2.

Fig. 4.  Solar irradiance and sunspot number in the era of satellite data.  Left scale is the energy passing through an area perpendicular to Sun-Earth line.  Averaged over Earth’s surface the absorbed solar energy is ~240 W/m2, so the full amplitude of the measured solar variability is ~0.25 W/m2.

imbalance, which has grown to about +0.75 ± 0.25 W/m2 over the past several decades due to increasing atmospheric greenhouse gases.[5],[6] However, the solar variability is not negligible in comparison with the energy imbalance that drives global temperature change.  Therefore, because of the combination of the strong 2016 El Niño and the phase of the solar cycle, it is plausible, if not likely, that the next 10 years of global temperature change will leave an impression of a ‘global warming hiatus’.

      On the other hand, the 2017 global temperature remains stubbornly high, well above the trend line (Fig. 1), despite cooler than average temperature in the tropical Pacific Niño 3.4 region (Fig. 5), which usually provides an indication of the tropical Pacific effect on global temperature.[7]  Conceivably this continued temperature excursion above the trend line is not a statistical fluke, but rather is associated with climate forcings and/or feedbacks.  The growth rate of greenhouse gas climate forcing has accelerated in the past decade.[3]  There is also concern that polar climate feedbacks may accelerate.[8]

      Therefore, temperature change during even the next few years is of interest, to determine whether a significant excursion above the trend line is underway.

 

  Fig. 5.    Ni  ñ  o 3.4 and global temperature change during the past five years.

Fig. 5.  Niño 3.4 and global temperature change during the past five years.

Appendix

   Fig. A1.     Global surface temperature relative to 1880-1920 based on GISTEMP data.  (a) Annual and 5-year means since 1880, (b) 12- and 132-month running means since 1970.  Blue squares in (b) are calendar year (Jan-Dec) means used to construct (a).  Update of Fig. 2 in reference 3.

Fig. A1.  Global surface temperature relative to 1880-1920 based on GISTEMP data.  (a) Annual and 5-year means since 1880, (b) 12- and 132-month running means since 1970.  Blue squares in (b) are calendar year (Jan-Dec) means used to construct (a).  Update of Fig. 2 in reference 3.

  Fig. A2.   Global surface temperature with extrapolation of data limited to 250 km from observations.

Fig. A2.  Global surface temperature with extrapolation of data limited to 250 km from observations.

  Fig. A3.   Global temperature in the past 100 and past 50 years based on local linear trends. 

Fig. A3.  Global temperature in the past 100 and past 50 years based on local linear trends. 

References

[a] Earth Institute, Columbia University, New York, NY

[b] SciSpace LLC, New York, NY

[c] NASA Goddard Institute for Space Studies, New York, NY

[1] Hansen, J., R. Ruedy, M. Sato, and K. Lo, 2010: Global surface temperature change. Rev. Geophys., 48, RG4004, doi:10.1029/2010RG000345.

[2] The current GISS analysis employs NOAA ERSST.v5 for sea surface temperature, GHCN.v.3.3.0 for meteorological stations, and Antarctic research station data, as described in reference 1.

[3] Hansen, J., M. Sato, P. Kharecha, K. von Schuckmann, D.J. Beerling, J. Cao, S. Marcott, V. Masson-Delmotte, M.J. Prather, E.J. Rohling, J. Shakun, P. Smith, A. Lacis, G. Russell, and R. Ruedy, 2017: Young people's burden: Requirement of negative CO2 emissions. Earth Syst. Dynam., 8, 577-616, doi:10.5194/esd-8-577-2017.

[4] Hansen, J.E., and S. Lebedeff, 1987: Global trends of measured surface air temperature. J. Geophys. Res., 92, 13345-13372, doi:10.1029/JD092iD11p13345.

[5] von Schuckmann, K., M.D. Palmer, K.E. Trenberth, A. Cazenave, D. Chambers, N. Champollion, J. Hansen, S.A. Josey, N. Loeb, P.-P. Mathieu, B. Meyssignac, M. Wild, 2016: An imperative to monitor Earth's energy imbalance Nature Climate Change 6, 138-144, doi:10.1038/nclimate2876.

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