Global warming is the long-term rise in Earth’s average surface temperature caused primarily by the accumulation of human-emitted greenhouse gases. The strongest attribution studies find that human influence explains essentially all of the observed warming since the mid-20th century: for 1951–2010, the estimated human contribution was 0.6–0.8°C, compared with about 0.65°C of observed warming, while natural forcing and internal variability contributed little on average. (Knutson, 2017) A separate attribution analysis estimated 2020 warming at 1.22 ± 0.15°C above 1850–1900, with 1.15 ± 0.15°C human-induced; greenhouse-gas warming was partly offset by other human influences, especially aerosols. (Ribes, 2021) The main drivers are fossil-fuel combustion, cement production, deforestation and other land-use change, alongside methane and nitrous-oxide emissions from agriculture and energy systems. (Tulachom, 2016)

The warming is already altering physical and biological systems. Observed and expected consequences include glacier, snow, sea-ice and permafrost loss; sea-level rise; changing precipitation; more frequent or intense heat extremes; ecosystem disruption; biodiversity loss; and risks to food, water and human health. (Tulachom, 2016) The effects are uneven: Arctic regions warm especially rapidly, while societies that depend heavily on climate-sensitive agriculture or have fewer resources to adapt face greater exposure. (Singh, 2024) Short-term fluctuations, including the apparent 1998–2012 “hiatus,” do not contradict the long-term trend; changes in ocean heat uptake, natural variability and observational coverage help explain that interval, and newer datasets show stronger recent warming. (Medhaug, 2017)

Limiting further warming requires rapid, large emissions reductions across the energy system rather than a single intervention. Evidence from mitigation modeling identifies low-carbon electricity as a high-impact priority, combined with energy efficiency, electrification of transport and buildings, industrial decarbonization, methane reductions, and protection and restoration of forests and other carbon sinks. (Deetman, 2014) Buildings offer substantial cost-effective potential through efficiency improvements, particularly lighting and other measures that deliver the same energy services with less consumption. (Ürge-Vorsatz, 2007) Policies that have shown progress include renewable-energy deployment, vehicle fuel-efficiency standards, passenger-vehicle electrification and forestry measures, but replication of existing sectoral progress alone was estimated to cut emissions only about 20% below a current-policies pathway by 2030—insufficient for a cost-effective pathway below 2°C. (Fekete, 2020) The central implication is that mitigation and adaptation must proceed together: emissions cuts reduce the magnitude of future warming, while adaptation addresses impacts that are already unavoidable.