Here are four graphs that governments should think about.
The first graph is of ice core temperature data from Vostok in Antarctica for the past 422,000 years. Temperatures are shown as variation from surface temperature in 1999 of -55.5 degrees Celsius.
(From:- Petit, Jean-Robert; Jouzel, Jean (1999): Vostok ice core deuterium data for 420,000 years. PANGAEA, https://doi.org/10.1594/PANGAEA.55505)
We are living in an inter-glacial period of unusual warmth, the Holocene, but previous interglacials were 2 to 3 degrees warmer than the present. Between these brief interglacials are 100,000 year long glacial periods. As the US National Climatic Data Centre says, “Glacial periods are colder, dustier, and generally drier than interglacial periods.”
We are lucky to be living now- life would be pretty hard for the small population the world could support in a glacial period.
Graph 2 shows just the last 12,000 years. We are at the extreme right hand end.
Note that Vostok temperatures have fluctuated between +2 and -2 degrees relative to 1999.
There are several ways of identifying the start and end of interglacials. I have chosen points when Antarctic temperatures first rise above zero and permanently fall below zero relative to 1999. Graph 3 shows the length of time between these points for the previous three interglacials compared with the Holocene.
The Holocene has lasted longer than the previous three interglacials: and is colder.
Many scientists think glacial periods start when summer insolation at 65 degrees North decreases enough so that winter snowfall is not completely melted and therefore year by year snow accumulates. Eventually the area of snow (which has a high albedo i.e. reflects a lot of sunlight) is large enough to create a positive feedback, and this area becomes colder and larger. Ice sheets form, and a glacial period begins. This is a gradual process that may take hundreds of years.
Well before global temperatures decrease, the first sign of a coming glacial inception will be an increasing area of summer snow in north-eastern Canada, Baffin Island, and Greenland.
I could find no data for northern Canada or Baffin Island, but it is possible to deduce summer snow area for Greenland.
Graph 4 shows the minimum area of snow at the end of summer in Greenland. (Data from Rutgers University, calculated from North America including Greenland minus North America excluding Greenland.)
The area of unmelted snow at the end of summer in Greenland has grown by about 100,000 square kilometres in the past 30 years. At this rate Greenland will be completely covered in snow all year round in about 45 years.
Caution: there was no glacial inception in the Little Ice Age- other factors may be involved, cloudiness being one. Further, a 30 year trend is just weather, and may or may not continue- but with the Holocene already longer and colder than previous interglacials, summer snow cover is one indicator we ignore at our peril.
Cold is not good for life.
kenskingdom 