Global Satellite Temperature versus ENSO

With the current El Niño possibly peaking now it will be interesting to see when the satellite derived global temperature anomalies peak. If past history during the satellite era is any indication, the satellite indicated global lower tropospheric temperature anomaly could peak as much as 3 to 6 months after the El Niño Southern Oscillation (ENSO) peak. The latest monthly Multivariate ENSO Index (MEI) from the US National Oceanic and Atmospheric Administration (NOAA) indicates a slight downturn in the MEI for October compared to September, which could possibly indicate the peak was in September. However, we will have to wait another month or two to be more confident. If the peak was in September, this El Niño will rank as the third most intense of the satellite era based on the MEI, after the 1997-98 and 1982-83 events.

The University of Alabama at Huntsville (UAH) satellite derived monthly global temperature for the lower troposphere (TLT) anomaly estimates showed a sharp rise from September to October as shown with the MEI in Figure 1. Also shown are the Mauna Loa apparent sunlight transmission monthly averages to indicate significant volcanic effects on sunlight transmission through the atmosphere. Effects from reduced sunlight transmission are evident after the El Chichón and Pinatubo volcanic eruptions in April 1982 and June 1991 respectively, after which sharp drops can be seen in the TLT anomaly estimates. Most of the strongest El Niños have been followed by La Niñas with corresponding drops in TLT for as much as a year or two following.

Figure 1. Comparison of monthly UAH satellite temperature for the lower troposphere (TLT) anomaly estimates, NOAA Mulitivariate ENSO Index, and NOAA Mauna Loa Apparent Transmission (MLAT) of sunlight (click to enlarge)

For the latest monthly ENSO updates, see the ENSO page accessible from the menu bar at the top of this post.

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21st Century Global Temperature Trends

This analysis focuses on global temperature anomaly trends for our current 21^st century so far, beginning in 2001, as we approach the first 15 years. The previous post covered trends over the entire satellite weather data era back to 1979.

As mentioned in my previous post, there are three main relatively independent sources of global surface temperature anomaly estimates available, derived from:  the Global Historical Climate Network (and sometimes including additional land stations) coupled with sea surface temperature measurements (GHCN), global weather forecast model input data, and satellite estimates of lower tropospheric temperatures.  There are multiple groups that compile and publish estimates from these sources, but for simplicity, estimates from four of these groups are presented here.  For the GHCN related estimates, this analysis uses the US National Center for Environmental Information (NCEI) estimates and the Berkeley Earth Surface Temperature (BEST) estimates.  These are compared to the satellite estimates from the University of Alabama Huntsville (UAH) and global forecast system (GFS) estimates provided by the University of Maine (UM) Climate Change Institute (CCI).

I compiled and graphed monthly global temperature anomaly estimates from each of these four groups for the period 2001 through September 2015 and calculated linear regression trends to indicate the overall change over this period. The UM CCI GFS estimates in Figure 1 show the lowest trend at -0.0014 degrees Celsius (C) per month over the period of nearly 15 years, which corresponds to -1.68C per century if maintained. The next lowest trend, shown in Figure 2, is +0.00005C per month from the UAH satellite estimates, which corresponds to +0.06C per century if maintained. The second highest trend is +0.0006C per month for the BEST GHCN estimates shown in Figure 3, which corresponds to +0.72C per century. The highest trend of 0.0009C per month is from the NCEI GHCN estimates shown in Figure 4 and corresponds to +1.08C per century if maintained.

Figure 1. Global temperature anomaly trend for 1979-2015 based on UM CCI GFS monthly estimates.

Figure 2. Global temperature anomaly trend for 1979-2015 based on UAH satellite monthly estimates.

Figure 3. Global temperature anomaly trend for 1979-2015 based on BEST GHCN monthly estimates.

Figure 4. Global temperature anomaly trend for 1979-2015 based on NCEI GHCN monthly estimates.

The variation in these trends underscores the uncertainty in all of these approaches. I suspect that the satellite derived estimate of +0.06C per century is the best compromise among these estimates. I find it very interesting that the GFS derived estimate of -1.68C per century contrasts so greatly with the GHCN derived trends. This discrepancy provides further evidence that ongoing adjustments to the GHCN based estimates are pushing them farther away from reality. We have no way of knowing whether these trends will be maintained for a full century, but there is certainly no clear evidence of an upward trend so far this century despite continued rapid increases in carbon dioxide (CO2). The implication is that CO2 is not at all the driver for global temperature trends and does not warrant expensive efforts to control.

Satellite Era Global Temperature Trends

This analysis focuses on global temperature anomaly trends for the satellite era beginning in 1979. Prior to this time, data coverage over oceans was much more sparse and this problem is worse moving farther back in time. Since the oceans cover 71 percent of the earth’s surface, poor coverage over the oceans leads to great uncertainty in global temperature anomaly estimates and trends prior to the satellite era. Consequently, I have little confidence in any global temperature trend analyses that include estimates from before the satellite era.

As mentioned in my previous post, there are three main relatively independent sources of global surface temperature anomaly estimates available, derived from:  the Global Historical Climate Network (and sometimes including additional land stations) coupled with sea surface temperature measurements (GHCN), global weather forecast model input data, and satellite estimates of lower tropospheric temperatures.  There are multiple groups that compile and publish estimates from these sources but for simplicity, estimates from four of these groups are presented here.  For the GHCN related estimates, this analysis uses the US National Center for Environmental Information (NCEI) estimates and the Berkeley Earth Surface Temperature (BEST) estimates.  These are compared to the satellite estimates from the University of Alabama Huntsville (UAH) and global forecast system (GFS) estimates provided by the University of Maine (UM) Climate Change Institute (CCI).

I compiled and graphed monthly global temperature anomaly estimates from each of these four groups for the period 1979 through September 2015 and calculated linear regression trends to indicate the overall change over this period. The UAH satellite estimates in Figure 1 show the lowest trend at +0.0009 degrees Celsius (C) per month over the period of nearly 37 years, which corresponds to +1.08C per century if maintained. The next lowest trend, shown in Figure 2, is +0.0011C per month from the UM CCI GFS estimates, which corresponds to +1.32C per century if maintained. The second highest trend is +0.0013C per month for the NCEI GHCN estimates shown in Figure 3, which corresponds to +1.56C per century. The highest trend of +0.0014C per month is from the BEST GHCN estimates shown in Figure 4 and corresponds to +1.68C per century if maintained.

Figure 1. Global temperature anomaly trend for 1979-2015 based on UAH satellite monthly estimates.

Figure 2. Global temperature anomaly trend for 1979-2015 based on UM CCI GFS monthly estimates.

Figure 3. Global temperature anomaly trend for 1979-2015 based on NCEI GHCN monthly estimates.

Figure 4. Global temperature anomaly trend for 1979-2015 based on BEST GHCN monthly estimates.

My best guesstimate of uncertainty for global temperature anomaly estimates is at least plus or minus 0.3C to 0.5C and thus these trends appear to be significant, although with a fairly low confidence. I suspect that the satellite derived estimate of +1.08C per century is the most accurate of these estimates, followed by the GFS estimate of +1.32C per century, neither of which is especially alarming considering evidence of much larger century scale changes in temperatures in the past during our current Holocene epoch as previously described in this blog. Also, we have no way of knowing whether these trends will be maintained for a full century and so far for the first 15 years of the 21^st century, there is evidence that the upward trend could be ending or at least slowing. My next post will take a closer look at global temperature trends for the 21^st century so far.