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Atmospheric temperature fluctuations are the main influence on Arctic sea-ice variability, whereas other factors explain only 25% of variability, according to an analysis of Earth system model simulations.

Human activity alters the atmospheric composition, which leads to global warming. Model simulations suggest that reductions in emission of sulfur dioxide from Europe since the 1970s could have unveiled rapid Arctic greenhouse gas warming.

The slow instrumental-record warming is consistent with lower-end climate sensitivity. Simulations and observations now show that changing sea surface temperature patterns could have affected cloudiness and thereby dampened the warming.

Even if fossil-fuel emissions were to cease immediately, continued anthropogenic warming is expected. Here, observation-based estimates indicate there is a 13% risk that committed warming already exceeds the 1.5 K Paris target.

Changes in climate are amplified in the Arctic region. An analysis of the CMIP5 state-of-the-art climate models reveals that temperature feedbacks are the dominant factor in this amplification, whereas the change in reflectivity of the Earth’s surface as sea ice and snow melt makes only a secondary contribution.

Near-surface warming in the Arctic has been almost twice as large as the global average over the past few decades. The vertical structure of temperature change in this region during the late twentieth century is examined and evidence is found for temperature amplification well above the surface. The causes of this amplification aloft remain uncertain, as feedbacks associated with the recent reduction in snow and ice cover are unlikely to be the cause.

Using an energy budget approach to understanding decadal temperature trends, this study highlights that observational uncertainty exceeds energy–flux deviations that affect such trends. Thus the origin of recent warming slowdown is unidentifiable.

The El Niño/Southern Oscillation (ENSO) affects weather patterns worldwide. Numerical experiments with an Earth system model suggest that cloud feedbacks act to amplify ENSO variability by a factor of two or more.

The east–west gradient in equatorial Pacific sea surface temperature has strengthened, but models suggest the opposite in past and future climates. Model ensembles show that the observed trend can arise from internal variability but their gradient weakens in the long term, causing more climate warming.

The North Atlantic ocean warming hole has been linked to reduced tropical heat import. Model simulations show an anthropogenically forced increased heat export poleward from the region, by overturning and gyre circulation, and shortwave cloud feedback control the warming hole formation and growth.

Warming in climate simulations since about 1970, when aerosol cooling showed little variation, constrains the transient climate response to doubled atmospheric CO₂ levels to about 1.67 K, according to an analysis of this emergent constraint.

An iris effect in tropical cloud-cover was controversially proposed as a negative climate change feedback that is not represented in climate models. If such an effect exists, it could go some way to reconciling climate models and observations.

Changes in global mean surface temperature and polar amplification found in the CMIP6/PMIP4 model ensemble mean can be constrained with paleoclimate data, as suggested by comparisons for three past time periods between 21,000 and 50 million years ago.