This article documents notable events, research findings, scientific and technological advances, and human actions to measure, predict, mitigate, and adapt to the effects of global warming and climate change—during the year 2025.
Summaries
May: André Corrêa do Lago, director of the 2025 United Nations Climate Change Conference (COP30, in Brazil), said, "It is not possible to have [scientific] denialism at this stage, after everything that has happened in recent years. So there is a migration from scientific denial to a denial that economic measures against climate change can be good for the economy and for people." 20 May: a study published in BioScience said that climate change has joined overexploitation and habitat alteration, to become a third major threat to Earth's animals. June: the Energy Institute's Statistical Review of World Energy suggested that 2025 may be the beginning of a paradigm shift in which the energy transition is driven by pursuit of energy security through energy independence ("risk hedging" in a volatile and uncertain environment, and seeking "resilient, decentralized, and clean energy systems"), rather pursuing climate change mitigation per se.
Measurements and statistics
10 January: a summary from the Copernicus Climate Change Service stated that 2024 was the warmest year since records began in 1850, with an average global surface temperature reaching 1.6°C above pre-industrial levels, surpassing for the first time the 1.5°C warming target set by the Paris Agreement. The summary also stated that 2024 was the second consecutive year with the hottest global temperature, surpassing 2023 by +0.12°C. 21 January: a study published in Nature Climate Change concluded that at least 30% of the Arctic has become a net source of carbon dioxide. 28 January: a study published in Environmental Research Letters reported that global mean sea surface temperature increases had more than quadrupled, from 0.06K per decade during 1985–89 to 0.27K per decade for 2019–23, and projected that the increase inferred over the past 40 years would likely be exceeded within the next 20 years. 3 February: a study co-authored by James Hansen published in Environment concluded that the IPCC had underestimated the effect of aerosols' planet-cooling radiative forcing, after enactment of international regulation of maritime aerosol emissions in the 2020s designed to improve air quality. This underestimation of aerosols' effect was said to cause underestimation of climate sensitivity, Hansen etal. writing that the reduction in aerosols explains the unexpectedly large global warming experienced in 2023-2024. Figure 3. 10 February: a study published in Nature Climate Change shows that the first single calendar year above 1.5 °C relative to pre-industrial levels in 2024 indicates that most probably Earth has already entered the 20-year period that will reach the Paris Agreement limit — that is, a 20-year period with average warming of 1.5 °C. 24 February: a study published by the non-profit Initiative on GHG Accounting of War estimated that the three years of the Russian invasion of Ukraine had caused 230 MtCO2e (metric tons of carbon dioxide equivalent) emissions—citing warfare, buildings reconstruction, landscape fires, damage to energy infrastructure, refugee and civil aviation displacement. 7 March: a study by World Weather Attribution concluded that in a February 2025 heat wave, climate change made extreme heat at least 2°C hotter and at least ten times more likely. 21 March: on the first World Glaciers Day (established by the UN General Assembly), the World Meteorological Organization reported that five of the past six years witnessed the most rapid glacier retreat on record, and 2022-2024 witnessed the largest three-year loss of glacier mass on record. 14 April: a study published in the Proceedings of the National Academy of Sciences concluded that since 1940, global warming has tripled the number of days per year that the oceans experience extreme surface heat conditions, and is responsible for a 1°C increase in maximum intensity of marine heatwave events. 10 May: a study published in AGU Advances said that observations from space show that Earth's energy imbalance in 2023 reached values that were twice that of the best estimate from the IPCC, and cautioned that the ability to observe this imbalance is deteriorating because satellites are being decommissioned. 30 May: a study jointly published by Climate Central, the Red Cross Red Crescent Climate Centre, and World Weather Attribution concluded that in the preceding year, four billion people experienced at least thirty additional days of extreme heat because of climate change; and that in 195 countries and territories, climate change at least doubled the number of extreme heat days as compared to a world without climate change. 5 June (reported): for the first time, NOAA's Mauna Loa Observatory measured an atmospheric carbon dioxide concentration of over 430 parts per million. 16 June: a study published in Nature Communications found that higher temperatures (27.3°C vs. 6.4°C) were associated with a 45% higher probability of having obstructive sleep apnea on a given night. 18 June: a study published in Nature concluded that global warming reduces crop production by 4.4% of recommended caloric consumption for each 1°C of global warming, though adaptation measures can reduce losses. July: the International Renewable Energy Agency's Renewable Power Generation Costs 2024 said that on a levelized cost of electricity (LCOE) basis, 91% of new renewable utility-scale capacity delivered power at a lower cost than the cheapest new fossil fuel-based alternative. New onshore wind projects had an LCOE of $0.034/kWh, solar photovoltaic $0.043/kWh, and hydropower $0.057/kWh. 7 July: a study published in Nature Geoscience reported that changes in long-duration heatwaves increase nonlinearly with temperature, with increments of warming increasing the durations more than proportionately. 11 August: applying extreme event attribution, a study published in Nature Ecology & Evolution concluded that human-caused intensification of heat extremes caused a 25–38% reduction in global abundance of tropical birds from 1950 to 2020. 25 August: an article published in Nature Climate Change reported the results of a 15-year study that concluded that long-term exposure to heat waves accelerated the aging process, with manual workers, rural residents and participants from communities with fewer air conditioners being more susceptible to health impacts. 27 August: a study published in Nature Climate Change concluded that tropical deforestation-induced local warming is associated with 23,610–33,560 heat-related deaths per year. 3 September: noting that the planet's carbon sequestration capacity is not unlimited, a study published in Nature concluded that fully using Earth's geologic storage capacity would help limit global warming by only . 10 September: applying extreme event attribution to 213 historical heatwaves from 2000–2023, a study published in Nature concluded that human-caused climate change made the median of heatwaves in 2000–2009 about 20 times more likely than a pre-industrial baseline, and heatwaves in 2010–2019 about 200 times more likely. Specifically, the study concluded that fossil fuel and cement producers enabled 16–53 heatwaves that would have been virtually impossible in a preindustrial climate. 10 September: a study published in Nature attributed 3,400–7,400 acute deaths in North America and 37,800–90,900 chronic deaths in North America and Europe to PM2.5 (fine particulate matter) exposure from the 2023 Canadian wildfires. 7 October: Ember's Global Electricity Mid-Year Insights 2025 reported that in the first half of 2025, renewables overtook coal generation for the first time on record (34.3% vs. 33.1% of global electricity). 13 October: Global Tipping Points Report 2025 said that "warm-water coral reefs are crossing their thermal tipping point and experiencing unprecedented dieback".Lenton, T. M., Milkoreit, M., Willcock, S., Abrams, J.F., Armstrong McKay, D.I., Buxton, J.E., Donges, J.F., Loriani, S., Wunderling, N., Alkemade, F., Barrett, M., Constantino, S., Powell, T., Smith, S.R., Boulton, C. A., Pinho, P., Dijkstra, H.A. Pearce-Kelly, P., Roman-Cuesta, R.M., Dennis, D. (eds).
13 October: a global study of ~320,000 sleep-tracker users, published in the journal Sleep, found that high ambient temperatures (99th vs 50th percentile: 27.3 °C vs 12.2 °C) were associated with a mean sleep loss of approximately 15–17 minutes and a ~40 % increase in the probability of a short-sleep night. 16 October: the World Meteorological Organization's Greenhouse Gas Bulletin reported that from 2023 to 2024, atmospheric carbon dioxide increased by 3.5 ppm, constituting the largest single-year increase since measurements began in 1957. 28 October: The Lancet estimated that in 2022, 2.52 million deaths globally were attributable to ambient air pollution from burning fossil fuels. 12 November: a report from Amnesty International said that at least 2 billion people, including 520 million children, live within of fossil fuel infrastructure. 12 November: a report from the American Association for the Advancement of Science (AAAS) said that the remaining carbon budget to limit global warming to 1.5°C is "virtually exhausted"—equivalent to four years at 2025 emissions levels. May: an EIT Urban Mobility study of non-exhaust emissions published by the European Institute of Innovation and Technology said that because of regenerative braking, electric vehicles produce ~83% less brake dust than equivalent conventional vehicles, though their increased weight leads to 20% higher tire and road wear emissions. 9 December: a report from the Global Coral Reef Monitoring Network concluded that, from 1980 to 2024, Caribbean hard coral cover declined by 48%; and that, between 1985 and 2024, mean sea surface temperature over coral reef areas increased by +1.07°C. 9 January 2026: a report published in Advances in Atmospheric Sciences said that ocean heat content in 2025 had reached a new record for nine consecutive years.Pan, Y., Cheng, L., Abraham, J. et al. 22 January 2026: Ember's European Electricity Review 2026 reported that in 2025, wind and solar energy provided 30% of EU electricity, surpassing fossil power (29%) for the first time, and generating more power than fossil sources in 14 of 27 EU countries. 21 April 2026: Ember's Global Electricity Review 2026 said that, in 2025, clean power growth exceeded the rise in overall global electricity demand (fossil fuel generation declining), and that renewables overtook coal power. 28 July 2026: risk assessor First Street's Global Severe Convective Storm Risk Pricing Economic Exposure to a Rising Peril stated that cumulative insured losses from severe convective storms (SCS)—hail, damaging straight-line winds, tornadoes, and severe thunderstorms—overtook that of tropical cyclones, with $82 billion in economic losses and constituting nearly one-third of all natural catastrophe losses worldwide in 2025.
Natural events and phenomena 1 January: a study published in Science Advances concluded that faster flow of the Antarctic Circumpolar Current (ACC) at higher latitudes causes upwelling of isotopically light deep waters around Antarctica, likely increasing atmospheric carbon dioxide levels and thereby potentially constituting a critical positive feedback for future warming.