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concentrations have increased by 40 per cent since pre-industrial times, primarily
from fossil fuel emissions and secondarily from net land use change emissions.
The ocean has absorbed about 30 per cent of the emitted anthropogenic CO 2 ,
causing ocean acidification.
• Humaninfluenceontheclimatesystemisclear.Thisisevidentfromtheincreasing
greenhouse gas concentrations in the atmosphere, positive radiative forcing,
observed warming, and understanding of the climate system.
• Human influence has been detected in warming of the atmosphere and the ocean,
inchanges intheglobal water cycle, inreductions insnowandice, inglobal mean
sea level rise, and in changes in some climate extremes. It is extremely likely that
human influence has been the dominant cause of the observed warming since the
mid-twentieth century.
• Cumulative emissions of CO 2 largely determine global mean surface warming
by the late twenty-first century and beyond. Most aspects of climate change will
persist for many centuries even if emissions of CO 2 are stopped. This represents a
substantial multi-century climate change commitment created by past, present and
future emissions of CO 2 .
*Probability terms such as “likely”, “extremely likely” are italicized in the original
IPCC report, to imply statistical significance. Because the phrases are actually devoid of
statistical or scientific meaning such italics have not been reproduced in this summary
table.
Table 3: Primary science conclusions—NIPCC 2013, 2014
Physical science
• Neither the rate nor the magnitude of the reported late twentieth century surface
warming (1979-2000) lay outside normal natural variability, nor was it in any
wayunusualcomparedtoearlierepisodesinEarth'sclimatichistory.Furthermore,
solar forcings of temperature change are likely more important than is currently
recognised, and evidence is lacking that a 2°C increase in temperature (of
whatever cause) would be globally harmful.
• No unambiguous evidence exists for adverse changes to the global environment
caused by human-related CO 2 emissions. In particular, the cryosphere is not
melting at an enhanced rate; sea-level rise is not accelerating; no systematic
changes have been documented in evaporation or rainfall or in the magnitude or
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