Update: How Do You Tell If The Earth's Climate System "Is Warming"?

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Back in August I had a post by the title of “How Do You Tell If The Earth’s Climate System “Is Warming”? The post took note of the fact that, with a time series (like for temperature) that fluctuates up and down, you can always give a presentation that makes the trend look to be whatever you want it to be, so long as you get to pick the start date. If you want to make it look like the trend is up, you pick a start date where the value of the series is low; and if you want to make it look like the trend is down, you pick a start date where the value of the series is high. Nothing to it! With the earth’s climate system, you have nearly infinite numbers of years that you can go back to get the result you want. Those who want to convince you that the earth’s climate system “is warming” typically pick as their start date either the 1880s or the 1970s, both of which were notable low points in the temperature times series. The trick is so obvious that you would think that nobody could be fooled. But, among others, they seem to have bamboozled Google, which as that August post noted, had taken to including on YouTube videos involving climate skeptics a legend stating “Multiple lines of scientific evidence show that the climate system is warming.”

“Multiple lines of evidence”? Really Google, is there any “line of evidence” that matters as to whether something “is warming” or “is cooling” other than the temperature time series? They don’t enlighten us as to what that other “line of evidence” might be.

Anyway, enough months have now passed for another year to end, so we now have three full years since the most recent temperature peak, which occurred in January 2016. Here is the latest UAH satellite temperature graph for the lower troposphere, going from the time the satellites were launched (1979) to December 2018:

UAH_LT_1979_thru_December_2018_v6.jpg

The 0.25 deg C temperature anomaly of the latest value represents a decline of some 0.61 deg C from the peak anomaly of 0.86 deg C in January 2016. That 0.61 deg C decline is not small in the context of this series. The whole range on this chart from coldest month (-0.51 deg C in 1984) to warmest month (+ 0.86 deg C in 2016) is only 1.37 deg C; and the 0.61 deg C drop represents close to half of that.

According to Dr. Roy Spencer of UAH (publisher of the graph), 2018 came in as the 6th warmest in the 40 years of the satellite time series. That would still put 2018 among the warmer years. But it also means that five previous years were warmer, one of them being 1998 — a full 20 years ago.

A number of questions occur to me, as I’m sure they do to you:

  • To support the assertion that the earth’s climate system “is warming,” shouldn’t the temperature be higher each year over the preceding year?

  • CO2 emissions have been increasing year by year, and the amount of cumulative CO2 in the atmosphere has been increasing year by year. Isn’t that supposed to be the driving mechanism behind global temperature? How is it possible for temperature to decline, and by a rather significant amount, when CO2 has increased?

  • Obviously, there must be some force at work sufficient to overcome the increase in CO2. What is that force? How do you know that that force will not continue to overcome the influence of the CO2? Indeed, how do you know that that force, alone or in combination with some other forces known or unknown, will not so completely overcome the influence of CO2 as to bring on the next ice age?

  • How many years of temperature decline does it take before it is no longer appropriate to assert that the climate system “is warming”? I mean, we’re using the present tense here. Since when do we use the present tense in our language to mean “something that occurred more than three years ago but has not occurred for the last three years”?

You might be interested in the take of our various highly prestigious “scientific societies” on the question of whether the earth’s climate system “is warming.” You can find a compilation of summary statements on that subject at the NASA web site at this link. NASA’s page is titled “Scientific consensus: Earth's climate is warming.” (Side question: What is a page with that title still doing up two years into the Trump administration?). A few examples:

  • American Association for the Advancement of Science: "The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society."

  • American Medical Association: "Our AMA ... supports the findings of the Intergovernmental Panel on Climate Change’s fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant."

  • American Physical Society: "The evidence is incontrovertible: Global warming is occurring.”

OK, these guys are a little more slippery with the wording than just saying (along with Wikipedia, Google and NASA) that “the climate system is warming.” But clearly NASA wants you to think that the phrase “climate change is occurring” is functionally the same thing.

Unfortunately for these societies, the question of whether the earth “is warming” is really not a scientific question, but rather only one of appropriate use of the English language. I don’t know where the temperatures may go from here — and neither do they. But a full three years into an obvious cooling cycle, isn’t it time to recognize that this awkward use of language is no longer appropriate?