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Peter Pfleiderer @klimapeter.bsky.social · 03/09/2026

In Paris oder Wien war dieser Sommer wirklich extrem 🥵

Peter Pfleiderer @klimapeter.bsky.social · 03/09/2026

Der Sommer ist vorbei und wird uns in Erinnerung bleiben! In Leipzig gab es die krasse Hitzewelle Ende Juni. Der Sommer entspricht aber ungefähr dem, was wir beim jetzigen Fortschritt der globalen Erwärmung von einem Sommer erwarten sollten 😬 Deutlich schlimmere Sommer wären möglich 🫣

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Peter Pfleiderer @klimapeter.bsky.social · 17/08/2026

Despite all the differences in heat characteristics in 100-year summers we do not find a statistically significant change in the the temperature anomaly of 100-year summers: A 100-year summer in pre-industrial climate was 2.2C warmer than an average summer and this is the same in current climate.

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Peter Pfleiderer @klimapeter.bsky.social · 17/08/2026

🌂 Drier soils contribute to increasing summer heat 🌡️ Today, summers begin with less soil moisture, reducing evaporative cooling on sunny days. This creates a longer late-summer window when dry soils and favorable weather in combination can produce extreme heat.

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Peter Pfleiderer @klimapeter.bsky.social · 17/08/2026

Our analysis separates three drivers of summer heat: mean warming, a widening of the daily temperature distribution, and a stronger seasonal cycle. The wider distribution is partly linked to an intensified seasonal cycle, which is especially pronounced in 100-year summers.

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Peter Pfleiderer @klimapeter.bsky.social · 17/08/2026

The largest differences are found for long lasting hot periods. Late summer has warmed most, greatly increasing the number of very hot days. At the same time, hot days are becoming more clustered together, leading to longer periods of extreme heat.

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Peter Pfleiderer @klimapeter.bsky.social · 17/08/2026

The later part of the summer has warmed more than early summer -> it’s the already hot part of the summer that has warmed most! This increases the intensity of heat extremes and this intensification is even stronger in centennial summers (expected once every 100 years).

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Peter Pfleiderer @klimapeter.bsky.social · 15/01/2026

We evaluate the statistical and machine learning decomposition methods against nudged circulation simulations: we apply the decomposition to a freely running simulation and compare it's estimated dynamical component to a simulation without GHG forcing but circulation nudged to the tested simulation

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Peter Pfleiderer @klimapeter.bsky.social · 15/01/2026

Over the period 1979-2023 circulation changes have contributed considerably to the warming of European summers. Over the mid-latitudes, a wavelike pattern is apparent with alternating regions of circulation induced warming and cooling.

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Peter Pfleiderer @klimapeter.bsky.social · 20/11/2025

2025 was again a severe #hurricane season with 4 major hurricanes (3 cat 5 hurricanes). In terms of accumulated cyclone energy (ACE) it was slightly above a normal season. Seasonal forecasts (including ours 🥳) predicted the ACE well this year 💪

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Peter Pfleiderer @klimapeter.bsky.social · 20/11/2025

The slightly above average ACE matches very well with seasonal forecasts 🥳 seasonalhurricanepredictions.bsc.es/forecast/sea...

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Peter Pfleiderer @klimapeter.bsky.social · 19/11/2025

I'm to announce our session on Synoptic and Large-Scale Circulation Dynamics at #EGU26 www.egu26.eu/session/56938 ... and I'm looking forward to read your abstracts together with @mittermeierm.bsky.social Jan Stryhal, Christoph Beck, Ileana Bladé

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Peter Pfleiderer @klimapeter.bsky.social · 26/09/2025

How the estimates of extreme event attribution are affected by aerosols depends strongly on the region and on the timing of the studied event. But in most regions, it's worth considering the aerosols in the analysis.

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Peter Pfleiderer @klimapeter.bsky.social · 26/09/2025

The same applies for other regions and we show that considering aerosol optical depth in the probabilistic extreme event attribution approach considerably improves the estimates.

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Peter Pfleiderer @klimapeter.bsky.social · 26/09/2025

Over Germany, heatwaves were dampened during a period of high aerosol emissions between 1950-2000. In a standard extreme weather attribution analysis that only considers global mean temperature, this effect of the aerosols is neglected -> with implications for the estimates

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Peter Pfleiderer @klimapeter.bsky.social · 07/05/2025

For 2025, we again expect high hurricane activity in the Atlantic. Most seasonal forecasts (including ours) estimate an accumulated cyclone energy of more than 120 ACE. Thanks to seasonalhurricanepredictions.bsc.es/forecast for collecting and publishing the forecasts!

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

In our paper, we also show how this approach can be applied to other end-user relevant impacts - for example extreme fire weather, or glacier loss.

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

For our example, different choices of critical risk levels would be possible. For instance, if one wants to be on the safe side (higher risk aversion) the acceptable cumulative CO2 emissions are substantially reduced.

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

In our paper, we also show how this approach can be applied to other end-user relevant impacts - for example extreme fire weather, or glacier loss.

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

The usefulness of reversing the impact chain relies on the ability to identify critical risk levels. A critical risk level is informed by our understanding of hazard, exposure and vulnerability but also by adaption options and limits as well as value judgements -> different choices are possible

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

By reversing the impact chain, we find that this could emerge for a carbon budget between 500 and 1200 Gt of CO2 between 2020 and 2050. This carbon budget depends on our level of risk aversion. For reference: 500 Gt is what the IPCC AR6 assessed as the central remaining carbon budget for 1.5°C.

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

Illustrative Example: An 50% increase in hot summer days might constitute a substantial health hazard for Berlin. In the forward impact chain, we would find that under a SSP1-26 scenario it is likely that the relative increase in hot days ranges between 20-110%. What do we make out of this? 🤔

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

In order to make sense of this scenario information, end-users need to be experts in the ‘upstream’ climate science. Many aren’t. And, as we argue, don’t have to be. They are experts in what constitutes critical climate risks. We propose to start there with our reversal approach. How does it work?

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Peter Pfleiderer @klimapeter.bsky.social · 03/01/2025

When studying climate impacts we go from emission (cause) through changes in the climate system and climatic impact-drivers towards the impacts (consequences). In each step uncertainties add up leading to large uncertainties in the socio-ecological impacts most people are interested in.

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Peter Pfleiderer @klimapeter.bsky.social · 02/12/2024

The Atlantic #hurricane season is over. It has been a highly active season with an ACE index of 162 (Accumulated Cyclone Energy). This outcome lies well within the range of our June #forecast of 133-220 ACE. Other forecasting groups expected a higher activity with an average of 211 ACE

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Peter Pfleiderer @klimapeter.bsky.social · 11/04/2024

Based on our seasonal #hurricane #forecast model we expect a highly active season in 2024 with an estimate of 160 ACE (accumulated cyclone energy). Other research institutes (ECMWF and CSU) forecast even higher activity

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Peter Pfleiderer @klimapeter.bsky.social · 22/01/2024

For precipitation, there are more diverse behaviors with some models showing a continued trend in precipitation in the period after peak warming irrespective of the cooling global mean temperatures.

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Peter Pfleiderer @klimapeter.bsky.social · 22/01/2024

The warming in surface air temperatures before peak warming is only partially reversed in the cooling period after peak warming for many oceanic regions. In contrast, the warming over many land regions is overcompensated in the period after peak warming.

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Peter Pfleiderer @klimapeter.bsky.social · 22/01/2024

The rate of change in regional temperature & precipitation with respect to changes in global mean temperatures (GMST) differs between the decades before and after peak warming. Leading to differences in regional climate signals between before and after peak warming at the same global warming level.

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Peter Pfleiderer @klimapeter.bsky.social · 22/01/2024

We analyze a multi-model CMIP6 ensemble of simulations of the SSP1-19 and SSP5-34-OS scenarios.

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Peter Pfleiderer @klimapeter.bsky.social · 09/01/2024

Temperature overshoot: climate reversibility and its impacts across spatial and temporal scales Your chance to discuss temperature overshoots and their implications! #EGU #EGU24

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Peter Pfleiderer @klimapeter.bsky.social · 30/11/2023

The Atlantic #hurricane season ends today with an accumulated cyclone energy of 144 ACE. Once again we are satisfied with our early June seasonal #forecast of 94-181 ACE The observed ACE is also in range of our early April we forecast (60-149 ACE)

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Peter Pfleiderer @klimapeter.bsky.social · 30/11/2023

Submit to our temperature overshoot #EGU24 session! "Temperature overshoot: climate reversibility and its impacts across spatial and temporal scales" convened by: Norman Steinert, @etheokritoff.bsky.social, Fabien Maussion, Biqing Zhu meetingorganizer.copernicus.org/EGU24/sessio...

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