From Tallbloke’s Talkshop

September 18, 2023 by oldbrew

The study, entitled The Detection and Attribution of Northern Hemisphere Land Surface Warming (1850–2018) in Terms of Human and Natural Factors: Challenges of Inadequate Data (August 2023), has 40 authors, some of whom are regular contributors to the ‘climate debate’ both in published papers and elsewhere. It takes a critical look at recent IPCC reports and summaries, especially the quality or otherwise of some of the data used to support its assertions. It suggests ways some of these issues could/should be addressed. Below is the abstract and the closing summary.
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Abstract
A statistical analysis was applied to Northern Hemisphere land surface temperatures (1850–2018) to try to identify the main drivers of the observed warming since the mid-19th century.

Two different temperature estimates were considered—a rural and urban blend (that matches almost exactly with most current estimates) and a rural-only estimate. The rural and urban blend indicates a long-term warming of 0.89 °C/century since 1850, while the rural-only indicates 0.55 °C/century.

This contradicts a common assumption that current thermometer-based global temperature indices are relatively unaffected by urban warming biases.

Three main climatic drivers were considered, following the approaches adopted by the Intergovernmental Panel on Climate Change (IPCC)’s recent 6th Assessment Report (AR6): two natural forcings (solar and volcanic) and the composite “all anthropogenic forcings combined” time series recommended by IPCC AR6. The volcanic time series was that recommended by IPCC AR6.

Two alternative solar forcing datasets were contrasted. One was the Total Solar Irradiance (TSI) time series that was recommended by IPCC AR6. The other TSI time series was apparently overlooked by IPCC AR6.

It was found that altering the temperature estimate and/or the choice of solar forcing dataset resulted in very different conclusions as to the primary drivers of the observed warming.

Our analysis focused on the Northern Hemispheric land component of global surface temperatures since this is the most data-rich component. It reveals that important challenges remain for the broader detection and attribution problem of global warming:
(1) urbanization bias remains a substantial problem for the global land temperature data;
(2) it is still unclear which (if any) of the many TSI time series in the literature are accurate estimates of past TSI;
(3) the scientific community is not yet in a position to confidently establish whether the warming since 1850 is mostly human-caused, mostly natural, or some combination.

Suggestions for how these scientific challenges might be resolved are offered.
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In summary, to resolve the causes of the climate changes since the 19th century more satisfactorily, we encourage more research into the following:
1. Better quantification of the contribution of urbanization bias to current global temperature estimates.
2. Improving temperature homogenization techniques to minimize urban blending and more accurately correct for other non-climatic biases.
3. Establishing which (if any) of the current TSI datasets are most reliable. We see this as involving two distinct periods: the satellite era and the pre-satellite era. We propose that further satellite missions could help improve the former, while more sun-like star projects could help improve the latter.
4. Consideration of the possibility that current estimates of the anthropogenic contribution to recent climate change might be too high.
5. Natural climate change drivers other than TSI and volcanic activity.

Full study here.