The current melting of Arctic sea ice:
Arctic sea ice has been retreating rapidly in recent years. Satellite observations show since 1979 a loss of almost 1 million square kilometres per decade in summer sea-ice extent, while simulations of Arctic sea-ice and sparse observational data also suggest a very rapid loss of ice thickness.
However, the actual magnitude of the overall loss is still somewhat uncertain because of observational constraints. It is clear, however, that the observed retreat is too large to be explicable by internal variability.
In addition, feedbacks cannot explain the magnitude of the retreat either, which hence must be driven by changes in the external forcing. Solar radiation has decreased over recent years, which would imply an increase in sea-ice coverage, opposite to what has been observed.
The most likely driver of the observed changes is hence the increase in atmospheric greenhouse gas concentrations that is mainly caused by anthropogenic burning of fossil fuels.