October 2018 Global Temperature Update

October 2018 Global Temperature Update

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October 2018 was the second warmest October since 1880.  At +0.99°C (relative to 1951-1980) it trailed only October 2015 (+1.08°C).

Extreme regional temperature anomalies in the Northern Hemisphere (see map), as much as +6-8°C in Siberia and minus 2-3°C in North America were evidently related to a wind anomaly carrying warm air in a northeasterly direction across Asia, with the balancing flow bringing Arctic air into North America.

Global temperature is beginning to rise as the tropical Pacific is in the early phase of an El Niño, only three years after the prior one.  It will be interesting to compare global temperature in coming months with 2015-16 temperatures (blue curve in the above figure for the rest of this year, then the green curve).

The record 2016 global temperature got a maximum boost from the Sun as 2016 was 1-2 years after Solar Maximum (link to http://www.columbia.edu/~mhs119/Solar/).  In contrast, 2019 will be during a deep Solar Minimum.

The record 2016 global temperature was boosted mainly by a ‘Super El Niño’, at least as judged by the usual Niño3.4 index, which matched or exceeded the 3.4 index for the 1997 Super El Niño.  We note, however, that recent high 3.4 indices (the 3.4 index is the temperature anomaly in a small region in the tropical Pacific) may be partly a result of a background global warming trend.

So it will also be interesting to see how strong this El Niño will be.  It may be that apparent El Niño strengths are boosted by global warming.

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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

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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.

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May 2018 Global Temperature Update

May 2018 Global Temperature Update

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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.

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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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