Here are excerpts from a paper commissioned in 2001:
The new paradigm of an abruptly changing climatic system has been well established by research over the last decade, but this new thinking is little known and scarcely appreciated in the wider community of natural and social scientists and policy-makers. At present, there is no plan for improving our understanding of the issue, no research priorities have been identified, and no policy-making body is addressing the many concerns raised by the potential for abrupt climate change. Given these gaps, the US Global Change Research Program asked the National Research Council to establish the Committee on Abrupt Climate Change and charged the group to describe the current state of knowledge in the field and recommend ways to fill in the knowledge gaps.
Recent scientific evidence shows that major and widespread climate changes have occurred with startling speed. For example, roughly half the north Atlantic warming since the last ice age was achieved in only a decade, and it was accompanied by significant climatic changes across most of the globe. Similar events, including local warmings as large as 16°C, occurred repeatedly during the slide into and climb out of the last ice age. Human civilizations arose after those extreme, global ice-age climate jumps. Severe droughts and other regional climate events during the current warm period have shown similar tendencies of abrupt onset and great persistence, often with adverse effects on societies.
Large, abrupt climate changes have affected hemispheric to global regions repeatedly, as shown by numerous paleoclimate records (Broecker, 1995, 1997). Changes of up to 16°C and a factor of 2 in precipitation have occurred in some places in periods as short as decades to years (Alley and Clark, 1999; Lang et al., 1999). However, before the 1990s, the dominant view of past climate change emphasized the slow, gradual swings of the ice ages tied to features of the earth’s orbit over tens of millennia or the 100-million-year changes occurring with continental drift. But unequivocal geologic evidence pieced together over the last few decades shows that climate can change abruptly, and this has forced a reexamination of climate instability and feedback processes (NRC, 1998). Just as occasional floods punctuate the peace of river towns and occasional earthquakes shake usually quiet regions near active faults, abrupt changes punctuate the sweep of climate history.
Paleoclimatic records show that large, widespread, abrupt climate changes have affected much or all of the earth repeatedly over the last ice-age cycle as well as earlier – and these changes sometimes have occurred in periods as short as a few years. Perturbations in some regions were spectacularly large: some had temperature increases of up to 16°C and doubling of precipitation within decades, or even single years. Changes in precipitation and evaporation are estimated to have caused changes in the extent of wetlands around the world of up to 50 percent. Agreement between proxy and instrumental records and between different proxy records lends confidence to paleoclimatic reconstructions and allows scientists to be very confident that abrupt climate change is a real, recurrent phenomenon.
The rest of the paper is now obviously quite dated. Research has progressed in leaps and bounds over the last decade and a half, as well as dramatic shifts already evident in the climate. (i.e., Arctic Ice loss)
But this paper shows how early we knew.
In 2015, the Met office declared we were 1 degree Celsius above the 1850-1900 pre-Industrial era. The period previously accepted as the reference period.
Immediately, NOAA and the World Meterological Organization changed their reference period to 1888-1910, which 'by coincidence' 'just happened' to knock .4 degrees Celsius off the chart, claiming it was done to 'improve accuracy'. And claimed we were .6 C above pre-industrial average.
The reason for doing such a thing would be an attempt to hide how serious this was and to give the politicians some wiggle room.
Now, one year later, NOAA and WMO are claiming we are 1.3 C above pre-industrial levels.
What no one is saying, whichever pre-industrial period you choose, Global temperatures increased .7 C between 2015 and 2016.