Facebook meme incorrectly claims past climate variations contradict human influence on current climate

The idea that 'climate change' is new or is caused by Humans is nonsense.
Flawed reasoning: The existence of "natural" climate changes in the past does not mean human activities are incapable of causing climate change today.
Fails to provide correct physical explanation: Multiple lines of evidence demonstrate that human-caused greenhouse gas emissions are causing global warming.
Many lines of evidence have enabled scientists to conclude that humans are responsible for global warming. Physics dictates that increased concentrations of greenhouse gases in the atmosphere trap additional heat in Earth's climate system, and human-caused emissions of greenhouse gases have increased those concentrations. Climate has changed in the past for a number of reasons, and studying those events helps scientists understand the way the climate system works.

AFFIRMATION COMPLETE: The environment of Earth has been continually changing for 4.5 billion years! The idea that 'climate change' is new or is caused by Humans is nonsense.

A meme that has been widely shared on social media claims that human influence on climate is nonsense because the climate has changed in the past.

Climate changes in Earth’s past are known because they have been studied by climate scientists and geologists. Past events have been caused by factors such as slow-changing cycles in Earth’s orbit, volcanic activity, and even the gradual motions of plate tectonics1.

Part of the understanding of Earth’s climate system comes from the study of past events. That understanding allows scientists to evaluate the climatic effects of human activities.

Currently, the concentrations of carbon dioxide and other greenhouse gases are increasing because of human-caused emissions, not something like volcanic eruptions or natural activity. And no matter the cause of increasing carbon dioxide, it results in a stronger greenhouse effect and warmer temperatures.

The 2017 US National Climate Assessment summarized the science on the cause of climate change this way: “This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.

The actions required to limit further climate change are more complicated than simply establishing a carbon tax. But whatever type of policy is used to encourage the transition, the physics of the climate system dictate that human-caused greenhouse gas emissions must be eliminated to halt the warming trend. If concentrations of greenhouse gases stop increasing, the amount of energy they trap in Earth’s climate system will also stop increasing.

Michael Henehan, Postdoctoral Researcher, GFZ Helmholtz Centre Potsdam:
[This comment comes from an evaluation of a similar claim.]
We are well aware that there are climatic fluctuations through geological time. Huge numbers of scientists study how the Earth’s climate has fluctuated before, and we know what caused those changes. Current warming is not related to any natural climate cycle, or process, or astronomic phenomenon.

Richard Betts, Professor, Met Office Hadley Centre & University of Exeter:
[This comment comes from an evaluation of a similar claim.]
The Earth’s climate has always varied, even before humans began to influence it. Climate scientists have always been very clear about this. But human-caused emissions of CO2 and other greenhouse gases have now added a new cause of climate change in addition to the existing causes of natural climate variability.

Mark Richardson, Postdoctoral scholar, Jet Propulsion Laboratory, California Institute of Technology:
[This comment comes from an evaluation of a similar claim.]
Here are logically identical arguments: “England scored goals before Harry Kane, so Harry Kane can’t score goals” Or in American English: “The New England Patriots scored touchdowns before Rob Gronkowski, so Rob Gronkowski can’t score touchdowns”. Or more simply: “Fires happened before humans, so humans can’t cause fires”.So if you agree with this logic and that humans aren’t causing CO2 to rise, you also have to believe that Harry Kane and Rob Gronkowski never scored anything and could never score anything, and that no fire has been caused by a human ever.Human-caused global warming, goals by Harry Kane, touchdowns by Rob Gronkowski, and fires set by people are all in the same boat. We have enormous evidence that they exist.

Patrick Brown, Postdoctoral Research Scientist, Carnegie Institution for Science:
[This comment is taken from an earlier review of a similar claim.]
The primary empirical evidence that greenhouse gasses cause global warming is the absorption (as a function of wavelength of radiation) of gasses like CO2, CH4 and N2O. This was discovered in 1859 by John Tyndall and has become a part of fundamental physics. Anyone can check this empirical relationship at any time with an absorption spectroscopy device.

The empirical evidence that increases in greenhouse gas concentrations (from fossil fuel burning) are the primary cause of century-scale warming is that observed global temperatures have risen in line with what would be expected from the observed increase in greenhouse gas concentrations and observations of natural drivers of climate change (e.g. solar output and volcanic eruptions) indicate that natural drivers are not causing warming.

Baird Langenbrunner, Postdoctoral scholar, University of California, Irvine:
[This comment is taken from an earlier review of a similar claim.]
First, greenhouse gases are well studied, and their properties are nonnegotiable: They absorb and re-emit longwave radiation, whether they’re in a laboratory setting or in the real atmosphere. To back this up with historical evidence, scientists have known since the 1860s that CO2 is a greenhouse gas and since the 1890s that this will affect the heat budget of the Earth through warming. Even then, these claims were based on empirical evidence, and they’re supported by decades of laboratory research.

Second, the link between increased greenhouse gas concentrations and warming continues to be supported by research in the last two decades. One study from 2001[1] used satellites to measure the type of energy entering and exiting Earth’s atmosphere and concluded that increases in greenhouse gases were responsible for extra heat measured between 1970 and 1997. The authors state that their results “provide direct experimental evidence for a significant increase in the Earth’s greenhouse effect that is consistent with concerns over radiative forcing of climate.” (Here, the term “radiative forcing” refers to the extra energy trapped in the atmosphere by greenhouse gases, cause warming.) A more recent study[2] arrived at similar conclusions, confirming predictions of the greenhouse effect in Earth’s atmosphere and providing “empirical evidence of how rising CO2 levels … are affecting the surface energy balance.” In other words, rising CO2 was linked directly to warming, even when things like plant uptake of CO2 were considered.


Publié le: 13 Jan 2020 | Editeur:

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