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Much has been written and argued, from all sides in the global warming debate, about the meaning of the asserted 17-year pause in global warming. Is a 17-year pause significant? Is a pause even occurring? Does the pause signal a longer-term halt to global warming or even a long-term cooling trend? Would a resumption of global warming to pre-pause rates end the global warming debate? A look at recent temperatures and their appropriate context provides helpful meaning to the much-discussed global warming pause.
Satellite instruments began uniformly measuring temperatures throughout the Earth’s lower atmosphere in 1979. Climate scientists overseeing these NASA satellite instruments produced the chart below showing the following temperature trends:
- a plateau of temperatures, with absolutely no warming, from 1979 through 1997
- a large temperature spike in 1998
- a return to the 1979-1997 mean in 1999-2000
- a modest escalation of temperatures in 2001
- an elevated plateau of essentially flat temperatures from 2002-2014
If we choose a starting point of mid-1998, the planet has cooled during the past 16 years. If we choose a starting point of late 1997 or early 1999, temperatures have been flat during the past 15 and 17 years. Examining the totality of the 35-year temperature record, we see approximately 1/3 of 1 degree Celsius warming during the period. Accordingly, global warming has occurred at a pace of approximately 1 degree Celsius per century over the duration of the satellite record.
Remote Sensing Systems (RSS) also compiles data from the satellite instruments, though RSS measures a slightly different range of the lower atmosphere. RSS reports a similar temperature history, available here. In the RSS compilation, we see not just a recent temperature plateau, but actual cooling. Again, the pace of warming throughout the entirety of the record is approximately 1 degree Celsius per century.
So what can we glean from the temperature data? Thirty-five year temperature trends are likely more meaningful than 17-year temperature trends. Nevertheless, 17-year temperature trends are nothing to sneeze at. Either way, whether the global temperature pause continues or not, temperatures have risen much more slowly than United Nations computer model predictions.
Computer models, of course, are only as accurate as their programmed data, formulas, and assumptions. The United Nations Intergovernmental Panel on Climate Change (IPCC) acknowledges there are many components to climate change for which climate scientists are merely making their best guesses. The IPCC-affiliated scientists have made guesses that the unknown climate components will dramatically accelerate the modest warming caused directly by human carbon dioxide emissions. So-called climate skeptics have argued the UN guesses consistently overestimate the warming propensity of the unknown climate components.
The real-world temperature data appear to support the skeptics. Even before the recent global warming pause, temperatures were warming at a relatively modest pace. The ongoing global warming pause is rendering the longer-term pace of warming still more modest.
IPCC computer models dating from 1990 through the present have consistently predicted at least 2.4 degrees of global warming per century. Such warming would require at least 0.24 degrees Celsius per decade, for which we should see at least 0.80 degrees Celsius warming since 1979. However, real-world warming since 1979 is occurring at less than half that pace. And there has been absolutely no real-world warming during the past 17 years.
IPCC adherents claim short-term variance is masking longer-term climate trends. According to this line of reasoning, the 35 years since 1979 are simply not long enough to form meaningful conclusions about the longer-term pace of global warming. This line of argument is unpersuasive for two important reasons: First, the admittedly less reliable ground-based mercury temperature readings from the mid-1940s through the late 1970s reported global cooling during the three decades immediately prior to the satellite era. Accordingly, the time period for which real-world temperatures are not rising nearly as rapidly as IPCC predictions is now not just 35 years, but approximately 70 years. Second, and even ignoring the 1940s-1970s global cooling, for global temperatures to meet IPCC’s predicted 2.4 degree rise by late this century, global temperatures must immediately – and that means immediately – begin rising at a sustained 0.30 degrees Celsius per decade. That has never come close to occurring during our modern warm period, and the ongoing global warming pause suggests that is unlikely to begin happening any time in the foreseeable future, either.
The El Nino/La Nina oscillation, moreover, provides some interesting context to the Earth’s recent temperature history. El Ninos warm the global climate while La Ninas cool the global climate. The 1998 global temperature spike was associated with the strongest El Nino in modern history. Also, El Ninos dominated the global climate from the late 1970s through the mid-2000s. Since 2007, however, modest La Nina conditions have prevailed.
The ongoing global warming pause is likely being assisted by the recent modest La Ninas. At some point between now and 2030, however, the cycle should flip back to one dominated by El Ninos. When that occurs, it is likely that global temperatures will again rise.
The ongoing global warming pause and the longer-term temperature record, however, indicate any future El Nino-assisted temperature rise will likely be modest once again. If the IPCC’s guesses on unknown climate components were correct, global temperatures would still be rising – even during this La Nina phase – at a fairly rapid pace. Moreover, global temperatures should have risen much more rapidly than was the case during the last El Nino phase. If IPCC model predictions were relatively accurate, global warming should be occurring at a pace of approximately 0.15 degrees Celsius per decade during La Ninas and approximately 0.35 degrees Celsius per decade during El Ninos. Neither has even come close to occurring in the real-world temperature record.
Pulling this all together, we can reach the following conclusions:
- The global warming pause is real.
- The global warming pause is significant.
- The global warming pause is not likely to be permanent.
- A future resumption of global warming at pre-pause rates – or even modestly accelerated rates – would not validate IPCC global warming predictions, and would instead continue to undermine the IPCC’s predictions of very rapid 21st century global warming.
- The most meaningful aspect of the global warming pause isn’t that temperatures have flattened for 17 years, but rather that the global warming pause extends and solidifies the longer-term record of smaller-than-predicted global temperature rise.
[Originally published at Forbes]