'After taking out the effect of ENSO and eruptions, it is apparent that temperatures have been flat since the early 1990’s; indeed they have arguably been falling since. This is significant. We are often told that the 17-year pause, with which we are all familiar, is solely dependent on cherry picking the big El Nino year of 1998 as a starting point. What Santer’s study shows is that there has been no underlying upward trend in global temperatures for more than 20 years.'
'The United Nations Intergovernmental Panel on Climate Change (IPCC) concluded that global mean temperature [changes] cannot be forecast because climate is too complex. They nevertheless rely on complex computer modelling to represent their assumptions about how the climate works. The outputs of such models are called “scenarios.” In effect, the IPCC tells stories, illustrated with computer graphics, about what would happen if their assumptions were correct.'
Georgia Institute of Technology's Dr. Judith Curry on April 15, 2015 at The House of Representatives Committee on Science, Space and Technology Hearing on the President’s UN Climate Pledge: 'Recent data and research supports the importance of natural climate variability and calls into question the conclusion that humans are the dominant cause of recent climate change. This includes:
The slow down in global warming since 1998
Reduced estimates of the sensitivity of climate to carbon dioxide
Climate models that are predicting much more warming than has been observed so far in the 21st century
We have made some questionable choices in defining the problem of climate change and its solution:
The definition of ‘dangerous’ climate change is ambiguous, and hypothesized catastrophic tipping points are regarded as very or extremely unlikely in the 21st century
Efforts to link dangerous impacts of extreme weather events to human-caused warming are misleading and unsupported by evidence.
'An explosive eruption large enough to cause huge numbers of deaths, alter the climate and poison the atmosphere occurring by the end of the century...The ash cloud thrown out from this eruption reached more than 26 miles (43km) into the atmosphere and triggered temperature changes that led to widespread famine and epidemics. The summer following the Tambora eruption is known as 'the year without summer'.
According to the 1990 IPCC Report, an additional 0.5C global warming would need to be observed before natural variability could be distinguished with high confidence from an "enhanced greenhouse effect" due to man-made emissions. However, as an article today at Reason.com points out,
"...enhanced greenhouse warming above the noise of natural climate variability would not yet have crossed over the benchmark (+0.5°C) set by the IPCC back in 1990. Interesting."
Satellite data indicates only ~0.2C warming since 1990, considerably short of the 0.5C threshold the IPCC set for itself in 1990 to determine whether additional global warming was within natural variability.