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and other insights from observations and theory were used to assess global
warming projections.
From the First to the Sixth Reports (Arias et al., 2021) and the Special Reports
that were produced from 1990 to 2023, the IPCC has evaluated relevant new
scientific evidence to go into each report, building a better understanding of the
climate system and the evidence that reveals of how the system is changing and
will change, and the anthropogenic responsibility in the climate change. The
IPCC's six assessment cycles since its beginning have comprehensively and
consistently presented the accumulated evidence of a changing climate system,
the Fourth Report published in 2007 was the first to conclude with high
statistical certainty that climate system warming is unequivocal.
Evidence has been documented with an increasing level of certainty to reveal
that recent climate changes such as the continued loss of ice around the world,
the increase in ocean heat content, the rise in sea levels, and deep-ocean
acidification, they are unprecedented in a context of hundreds of thousands of
years.