Monthly Trends

Last updated 2017 December 1 to include preliminary November estimates based on preliminary daily estimates for the entire month.

The latest monthly global surface temperature anomaly estimates from Climate Forecast System Reanalysis (CFSR) output provided by the University of Maine Climate Change Institute (UM CCI) are graphed below.  The CFSR is based on output from the Global Forecast System (GFS) which is initialized and run four times each day for routine weather forecasting.  Monthly estimates through May 2017 are based on final monthly estimates from UM CCI.  The monthly estimates for June through October 2017 are based on final daily averages and the estimates for November 2017 are based on preliminary daily estimates and thus these estimates may change slightly once final monthly averages are released.

The monthly UM CCI CFSR global temperature anomaly estimates have been shifted from the non-standard 1979-2000 reference period used by UM CCI to the most recent standard climatological reference period of 1981-2010 based on monthly averages for those periods.  The monthly reference period shifts range from -0.09C for June through August to -0.16C for November and average -0.12C for the year.

The graph below shows the monthly estimated global surface temperature anomaly trend for the 21st Century so far (since 2001) from the CFSR adjusted for changes from Version 1 to Version 2.  The current trend for this period is 0.00154C per month or 0.0185C per year and 0.554C if maintained for 30 years and to 1.85C if maintained for the entire century.  Since this trend is based on 16 years of data, the projected trend is not likely to be very accurate beyond 10 to 20 percent of the observational period, which corresponds to only about two or three years.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The graph below shows the unadjusted CFSR monthly estimated global surface temperature anomaly trend for the 21st Century so far (since 2001).  The current trend for this period is -0.00008C per month or -0.0010C per year and -0.029C if maintained for 30 years and to -0.10C if maintained for the entire century.  Since this trend is based on 16 years of data, the projected trend is not likely to be very accurate beyond 10 to 20 percent of the observational period, which corresponds to only about two or three years.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The latest CFSR adjusted monthly global temperature anomaly estimates since 1979 are graphed below. The trend in estimated global temperature anomalies since 1979 is +0.00147C per month, +0.0176C per year, +0.529C per 30 years, and to +1.76C if maintained for 100 years.  Since this trend is based on 38 years of data, the projected trend is not likely to be very accurate beyond 10 to 20 percent of the observational period, which corresponds to about 4 to 8 years.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The latest CFSR (unadjusted) monthly global temperature anomaly estimates since 1979 are graphed below. The trend in estimated global temperature anomalies since 1979 is +0.00120C per month, +0.0144C per year, +0.432C per 30 years, and to +1.44C if maintained for 100 years.  Since this trend is based 38 years of data, the projected trend is not likely to be very accurate beyond 10 to 20 percent of the observational period, which corresponds to about 4 to 8 years.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The UM CCI provides monthly estimates of global temperature by latitude zones, including the non-overlapping Arctic (60N-90N), Northern Hemisphere middle latitudes (30N-60N), Tropics (30N-30S), Southern Hemisphere middle latitudes (30S-60S), and Antarctic (60S-90S).  The temperature anomaly trends for these zones since 1979 are graphed below.  Note that the scale of the vertical axis changes from zone to zone.  Also note that the temperature trends progressively and consistently drop lower toward the south.

The trend in estimated Arctic zone (60N-90N) temperature anomalies since 1979 is +0.00433C per month, +0.0520C per year, or +1.559C per 30 years, and to +5.20C if maintained for 100 years.  The likelihood of this trend extending for 100 years appears to be very small based on evidence of past oscillations in temperature and ice cover over periods of about 30 to 40 years in the Arctic zone.  Thus, it is possible that Arctic temperatures will begin declining sometime in the next 5 to 10 years with the onset of the next cold phase.  This pattern may be associated with the Atlantic Multidecadal Oscillation (AMO) and its influence on sea surface water temperatures in the Arctic.  The Arctic zone only accounts for about 7 percent of the global surface area, but because of the very large anomalies that occur there, it can sometimes have a significant impact on the global average anomalies.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The trend in estimated Northern Hemisphere middle latitude (30N-60N) temperature anomalies since 1979 is +0.00196C per month, +0.0235C per year, or +0.706C per 30 years, and to +2.35C if maintained for 100 years.  The Northern Hemisphere middle latitude zone accounts for about 18 percent of the global surface area.

Final through May 2017 (click to enlarge)

The trend in estimated Tropical zone (30N-30S) temperature anomalies since 1979 is +0.00113C per month, +0.0136C per year, or +0.407C per 30 years, and to +1.36C if maintained for 100 years.  The large rise in temperature anomalies in 2015-2016 has likely been driven by the El Niño event and appears similar to the El Niño influences in 1987-1988, 1997-1998, and 2009-2010.  These events were all followed by strong La Nina events characterized by much lower tropical temperature averages.  Consequently, the tropical temperatures are likely to drop much lower later this year and may fall below the climatological average in 2017 as happened in 1988-89, 1999-2000, and again in 2011-2012.  The Tropical zone covers about 50 percent of the global surface area centered at the equator.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The trend in estimated Southern Hemisphere middle latitude (30S-60S) temperature anomalies since 1979 is +0.00049C per month, +0.0059C per year, or +0.176C per 30 years, and to +0.59C if maintained for 100 years.  The Southern Hemisphere middle latitude zone accounts for about 18 percent of the global surface area.

Final through May 2017 (click to enlarge)

The trend in estimated Antarctic zone (60S-90S) temperature anomalies since 1979 is -0.00164C per month, -0.0197C per year, or -0.590C per 30 years, and to -1.97C if maintained for 100 years.  The Antarctic zone only accounts for about 7 percent of the global surface area, but because of the very large anomalies that occur there, it can sometimes have a significant impact on global average temperature anomalies.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The pattern of temperature trends for the Southern Hemisphere middle latitudes and Antarctic is not consistent with hypothesized significant man-made global warming.  Since carbon dioxide concentrations are relatively uniform across the globe on a time scale of years and show persistent upward trends since 1979, these flat and downward temperature trends indicate that hypothesized man-made global warming is not dominant and that other factors are likely to be more dominant over the last 38 years.  The implication is that observed upward temperature trends in the Northern Hemisphere are also being dominated by other factors.  These other factors need to be resolved before any kind of accurate future climate predictions can be made.  Predictions made assuming that man-made global warming is dominant are likely to fail.

The temperature anomaly trends hide the seasonal cycles that occur.  The graphs below show the UM CCI CFSR average temperatures for the same latitude zones graphed above as temperature anomalies.  The CFSR estimated global monthly average temperature has a large seasonal cycle dominated by the Northern Hemisphere with a peak in July that is almost 4C higher than the minimum in January.  This seasonal variation dwarfs the annual anomaly trend.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

All of the latitude zones described above show seasonal temperature patterns as well.  The largest monthly average temperature variation by far is for the Arctic zone with a range of about 25C from winter to summer.  The Tropics zone exhibits the least variation at about 1C but has a double peak pattern with a secondary maximum and secondary minimum every year.  The Tropics average maximum is for April with secondary maximum for September, and the average minimum is for January with secondary minimum for July.  All other zones have seasonal patterns with maximums in zonal summer and minimums in zonal winter.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

Another way to look at temperatures is by the seasonal pattern.  The graphs below show the seasonal patterns for 2015 and 2016 so far compared to the most recent 1981-2010 standard climatological averages for each month based on the UM CCI CFSR data.  Below is the graph for global average temperatures by month.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

The Arctic zone (60N-90N) seasonal pattern is very similar to the global pattern, but much higher in amplitude.  Notice that monthly average temperatures in the Arctic zone are above freezing for four months from June through September.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

Monthly average temperatures in the Tropics zone (30N-30S) show little variation through the year but exhibit a weak seasonal pattern with primary peak in  April, secondary peak in September, primary minimum in January, and secondary minimum in July.  The 2015-2016 El Niño event is likely responsible for the rise in tropical temperatures relative to the climatological baseline beginning around May 2015.  This event appears to be peaking in its influence during the spring of 2016 and tropical temperature anomalies may decline through the remainder of 2016.  In August 2016 the monthly average temperature was lower than the corresponding monthly average in 2015 for the first time this year and has remained below 2015 each month since.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

Antarctic zone (60S-90S) monthly average temperatures peak well below freezing in January and on average show a minimum in August during winter as might be expected.  However, the 2016 minimum was in June and the 2015 minimum was in July, so there is some variation from year to year.

Final through May 2017 and preliminary for June through November 2017
(click to enlarge)

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