Reacción a "Reactions: skeletons of marine sponges suggest that global temperature has already exceeded the 1.5°C limit"

The way these findings have been communicated is flawed, and has the potential to add unnecessary confusion to public debate on climate change. Despite the headline, the results of this paper do not show that we have already exceeded the Paris climate targets.

“This paper presents a detailed sclerosponge record from the Caribbean that shows that ocean surface warming (something they term industrial-era warming) in this region began in the 1860s, a time earlier than the existence of good ocean temperature records. This finding is used to argue that the pre-industrial reference baseline should be pushed back to the period from the 1700s to 1860, rather than the 1850-1900 period usually used by the IPCC and others. With this new baseline, an extra 0.5C is added to our estimates of industrial-era warming, and hence the studies infers we are already well past 1.5C of industrial era warming and approaching 2.0C.

“While the Paris climate targets set reference warming targets against pre-industrial baselines, there is an implicit assumption this is dominated by human-caused warming caused by the industrial era. It is unlikely that warming of 0.5C in the 1800s is human-caused. By 1900 cumulative human fossil fuel/cement carbon emissions since 1750 were a mere 2.5 % of our cumulative emissions by 2021 (Source: Our World in Data). If we include land use change (much more uncertain) another few percent might be added. This is unlikely to have caused substantial warming compared to the 1.4C of warming caused by the remaining 97.5% of cumulative emissions.

“Hence this early industrial era warming, if real, is almost certainly not human-caused, is not industrial-caused warming. Our models of climate warming impacts are based on warming relative to 1850-1900, and moving the baseline definition of preindustrial does not make these expected impacts worse. Human-caused climate warming to date is still around 1.4C. It is the date of the reference period that matters rather than whether it is labelled pre-industrial or not. The period 1850-1900 is a period of relatively reliable global data when industrial era human-caused climate change was likely negligible.