Assessing the role of anthropogenic warming from temporally inhomogeneous historical data in the presence of large natural variability is difficult and has caused conflicting conclusions on the detection and attribution of tropical cyclone (TC) trends. [bold, links added]
Here, using a reconstructed long-term proxy of annual TC numbers together with high-resolution climate model experiments, we show robust declining trends in the annual number of TCs at global and regional scales during the twentieth century.
The Twentieth Century Reanalysis (20CR) dataset is used for reconstruction because, compared with other reanalyses, it assimilates only sea-level pressure fields rather than utilizing all available observations in the troposphere, making it less sensitive to temporal inhomogeneities in the observations.
It can also capture TC signatures from the pre-satellite era reasonably well.
The declining trends found are consistent with the twentieth-century weakening of the Hadley and Walker circulations, which make conditions for TC formation less favorable.
Human activities are estimated to have caused ~1.0 °C of global warming above pre-industrial levels, with most of the warming occurring since the mid-twentieth century1.
This warming may have already impacted the number of tropical cyclone (TC) occurrences at global and regional scales, but so far changes are unclear—and often controversial—due to several confounding factors, including data quality issues that create major challenges for detection and attribution of TC trends2.
Before the commencement of geostationary weather satellite monitoring in the 1970s, historical global ‘best track’ records of TCs were more prone to discontinuities and sampling issues and are therefore considered problematic for climate change trend analysis2,3.
TC observations have improved substantially since the 1970s, but this relatively short period of high-quality data does not provide consensus on the detection of trends or on the attribution of trends to anthropogenic influences.
On the basis of the few decades of reliable historical data, there is no clear evidence of an observed trend in global TC numbers.
Trends in regional TC numbers based on observations can be obscured by natural climate variability, including at decadal to multi-decadal time scales, leading to conflicting conclusions on the detection and attribution of TC frequency trends.
Read rest at Nature Climate Change
