https://rogerpielkejr.substack.com/p/the-bad-science-and-bad-policy-at
Remarkably, the Intergovernmental Panel on Climate Change (IPCC) and the U.N. Framework Convention on Climate Change (UN-FCCC, 1992) use different definitions of "climate change."
The IPCC defines climate change as:
A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions and persistent anthropogenic changes in the composition of the atmosphere or in land use.
Under the IPCC, any change in the statistics of weather, regardless of cause, is thus climate change.
In contrast, the UN-FCCC adopted a much narrower and scientifically inaccurate definition of climate change:
[A] change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.
Thus, under the UN-FCCC, the only change in the statistics of weather that count as "climate change" are those that result from human activity that alters the composition of the atmosphere. By "human activity that alters the composition of the atmosphere," the UN-FCCC explicitly means greenhouse gases, as you can see above from Article 2 of the UN-FCCC.
If the sun got just a bit brighter next year, leading to climate chaos and massive changes in global weather events for the next half-century, that would be climate change under the IPCC, but it would not under the UN-FCCC. If that sounds bizarre -- it is!
Under the UN-FCCC's limited definition of climate change, climate policy has evolved from a focus on direct measures of greenhouse gases -- such as emissions and atmospheric concentrations -- to a focus on global average surface temperature, formalized in the 2015 Paris Agreement under the UN-FCCC.
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The shift from a focus on greenhouse gases to global average temperatures occurred based on the belief that the only factor responsible for changes in the statistics of global temperatures was greenhouse gases -- so temperatures could serve as a proxy metric.
In 2017, Carbon Brief sought to explain why temperatures and greenhouse gas emissions were proxies:
Humans emissions and activities have caused around 100% of the warming observed since 1950, according to the Intergovernmental Panel on Climate Change's (IPCC) fifth assessment report. . . Since 1850, almost all the long-term warming can be explained by greenhouse gas emissions and other human activities.
The logic of the 2015 Paris Agreement was based on the assumption that greenhouse gas concentrations and global temperatures were simply interchangeable variables.
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The narrow definition of climate change of the UN-FCCC and its myopic policy focus on greenhouse gas emissions contributes to what Mike Hulme has called climate reductionism: "the ideology - the settled belief - that the dominant explanation of all social, economic and ecological phenomena is a human-caused change in the climate."
The UN-FCCC takes the reductionism even further by restricting "human-caused changes in climate" to only those associated with greenhouse gas emissions. If the big greenhouse gas emissions knob is the only policy control you have, then that will inevitably become a singular focus.
Climate policy has been steered into a political cul-de-sac by bad science and bad policy. The bad science can be found in the UN-FCCC's definition of climate change that is at odds with the scientifically-accurate definition of climate change of the IPCC. The bad policy results from the use of global average temperatures as a proxy for human flourishing, making cost-benefit analyses seem unnecessary or even unhelpful to the political cause.
Hulme asserts:
[T]here are some futures beyond 1.5 degrees C (or even 2 degrees C) that are more desirable than other futures which do not exceed these warming thresholds.
It is long overdue for climate policy discussions to take that seriously.