Let’s be Very Clear — 100 Percent (or More) of Recent Warming was Caused By Humans

“We actually have high confidence that the warming that is happening now is not natural cycle. If anything, over the past few decades, nature has tried to cool us off a little bit… The sun has dimmed just a little bit. We have blocked the sun with particles from our smokestacks just a little bit. And yet it has warmed. If you were to ask how much of the warming that we see recently has been caused by our greenhouse gasses, it’s a little more than all of it (emphasis added).” — Dr Richard Alley


To say that scientists, as a group, tend to be cautious is probably the understatement of the Century. In most cases, this caution is beneficial — preventing outrageous assertions regarding key issues and providing a stable basis for developing rational policy.

(Dr. Richard Alley, Dr Michael Mann, and Dr Johnathan Brockopp discuss the extent of the global warming crisis without false equivalency given to climate change deniers. Video source: Conversations — Live Climate Change.)

But when it comes to confronting climate change deniers, such caution and reticence has often been exploited by the fossil fuel interests and their political backers who tend to make intentionally deceptive arguments aimed at casting doubt on scientific findings. Just as Scott Pruitt, a man who has fought helpful emissions regulations by EPA at the behest of the fossil fuel industry for most of his legal career, did last week on CNBC’s Squawk Box when he said:

“I think that measuring with precision human activity on the climate is something very challenging to do and there’s tremendous disagreement about the degree of impact, so no, I would not agree that it’s [CO2] a primary contributor to the global warming that we see.”

Playing Disingenuous and Intentionally Deceptive Word Games

Pruitt’s statement was made with a pretty obvious intent to cast fallacious doubt on established scientific findings. It was deceptive. And it aimed at highlighting perceived, but not actual, uncertainties in the science. It ultimately perpetrated a logical fallacy of consistency (argument based on false equivalency). Such fallacies tend to exploit seeming gray areas in established understanding in order to cast doubt on solid evidence. In this case, to create a false sense that counter arguments against the scientific basis for CO2 as a heat trapping gas have equal weight to the actual science.

In the end, the perception of uncertainty is what false and fallacious arguments like Pruitt’s seek to generate. And these arguments often aim to exploit the fact that overarching scientific consensus statements seldom claim 100 percent certainty, even though findings, especially in the case of climate change, are highly accurate.

In one example, more than 97 percent of scientists agree that global warming is caused by humans. This consensus is among the strongest for any scientific finding. However, the most recent IPCC report found that:

“It is extremely likely [defined as 95-100% certainty] that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic [human-caused] increase in greenhouse gas concentrations and other anthropogenic forcings together.”

This statement, at its face value is a strong validation for the human warming consensus. However, it provides a bit of a linguistic loop-hole in the phrase — ‘more than half’ — which seems to imply that almost half of the warming Earth has experienced was caused by something other than human activity. This apparent but false uncertainty is the kind of statement that people like Pruitt, who use deceptive argumentation, tend to latch onto. And if a person were to make the conclusion that nearly 50 percent of warming was not caused by humans and that the ultimate cause of warming is therefore in doubt, then it would be a false one.

More Than 100 Percent of Recent Warming Caused By Humans, CO2 Earth’s Primary Temperature Control Knob

(Most recent warming attribution studies find that more than 100 percent of the atmospheric heat gain we’ve seen during the past 50-65 years was caused by human activity such as fossil fuel burning. Image source: Skeptical Science.)

The truth is that IPCC made a very cautious statement. It has 95 to 100 percent confidence that more than 50 percent of warming has been caused by human activity. And the basis for this statement is that most studies find that while natural factors like solar activity are pushing the world to cool, the human forcing is strong enough to overcome that natural cooling trend and to set in place a very strong and unnatural warming trend instead. The science finds that without the greenhouse gas emissions coming chiefly from fossil fuel burning, the Earth would have seen slowly falling temperatures over the past 50-150 years.

Moreover, studies for the past 50-65 years almost universally attribute 100 percent or more of warming to human produced heat forcing. The above graphic, by Skeptical Science, shows a sample of new studies in which 99 to 170 percent of recent warming was attributed to human causes.

(According to IPCC, carbon dioxide is the primary heat trapping gas emitted by humans and is responsible for the majority of atmospheric warming. Meanwhile, NASA scientists find that this gas is the chief control knob governing Earth’s temperature.)

In addition, the lion’s share of the heat trapping, according to the science, can be attributed to one greenhouse gas — CO2. For NASA, along with pretty much every other major scientific body studying climate, finds that CO2 is Earth’s primary temperature control knob.

So when Scott Pruitt, a climate change denier and Trump’s pick for head of the EPA says that there’s a lot of uncertainty about CO2 and it’s not the primary source of warming and that it’s uncertain whether humans are a factor — he’s telling a lie. The science is very clear that warming is human caused, that probably more than 100 percent of warming has been driven by human activity, and that CO2 from fossil fuel emissions has been the cause of the majority of that warming.

But in addition to telling a lie Pruitt, as head of EPA, is committing malfeasance. For he is the head of the agency responsible for regulating harmful gasses like CO2 and for preventing the severe damage that will surely be inflicted upon the American public if these gasses continue to be released into Earth’s atmosphere.


CNBC’s Squawk Box

Skeptical Science

IPCC Fifth Assessment

CO2: Principal Control Knob Governing Earth’s Temperature

Hat tip to Erik

Hat tip to Cate


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