Réseau Transition be

In a rapidly changing climate, evidence-based decision-making benefits from up-to-date and timely information. Here we compile monitoring datasets (published at https://doi.org/10.5281/zenodo.15639576; Smith et al., 2025a) to produce updated estimates for key indicators of the state of the climate system: net emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. This year, we additionally include indicators for sea-level rise and land precipitation change. We follow methods as closely as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One report.

Recent simulations using the Community Earth System Model (CESM) indicate that a tipping event of the Atlantic Meridional Overturning Circulation (AMOC) would cause Europe to cool by several degrees. This AMOC tipping event was found under constant pre-industrial greenhouse gas forcing, while global warming likely limits this AMOC-induced cooling response. Here, we quantify the European temperature responses under different AMOC regimes and climate change scenarios. A strongly reduced AMOC state and intermediate global warming (C, Representative Concentration Pathway 4.5) has a profound cooling effect on Northwestern Europe with more intense cold extremes. The largest temperature responses are found during the winter months and these responses are strongly influenced by the North Atlantic sea-ice extent. Enhanced North Atlantic storm track activity under an AMOC collapse results in substantially larger day-to-day temperature fluctuations. We conclude that the (far) future European temperatures are dependent o

Global temperature for 2025 should decline little, if at all, from the record 2024 level. Absence of a large temperature decline after the huge El Nino-spurred temperature increase in 2023-24 will provide further confirmation that IPCC’s best estimates for climate sensitivity and aerosol climate forcing were both underestimates. Specifically, 2025 global temperature should remain near or above +1.5C relative to 1880-1920, and, if the tropics remain ENSO-neutral, there is good chance that 2025 may even exceed the 2024 record high global temperature.

... An “acid” test of our interpretation will be provided by the 2025 global temperature: unlike the 1997-98 and 2015-16 El Ninos, which were followed by global cooling of more than 0.3°C and 0.2°C, respectively, we expect global temperature in 2025 to remain near or above the 1.5°C level. Indeed, the 2025 might even set a new record despite the present weak La Nina. There are two independent reasons. First, the “new” climate forcing due to reduction of sulfate aerosols over the ocean remains in place, and, second, high climate sensitivity (~4.5°C for doubled CO2) implies that the warming from recently added forcings is still growing significantly.

Improved knowledge of glacial-to-interglacial global temperature change implies that fast- feedback equilibrium climate sensitivity is at least ~4°C for doubled CO2 (2×CO2), with likely range 3.5-5.5°C. Greenhouse gas (GHG) climate forcing is 4.1 W/m2 larger in 2021 than in 1750, equivalent to 2×CO2 forcing. Global warming in the pipeline is greater than prior estimates. Eventual global warming due to today’s GHG forcing alone – after slow feedbacks operate – is about 10°C. Human-made aerosols are a major climate forcing, mainly via their effect on clouds. We infer from paleoclimate data that aerosol cooling offset GHG warming for several millennia as civilization developed. A hinge-point in global warming occurred in 1970 as increased GHG warming outpaced aerosol cooling, leading to global warming of 0.18°C per decade. Aerosol cooling is larger than estimated in the current IPCC report, but it has declined since 2010 because of aerosol reductions in China and shipping. Without unprecedented global actions to