Chapter 12: Alaskan Equivalent Latitude

In central Alaska and the Yukon Territory, azonal dry steppe is growing now only in a few warm basins and on well-drained south-facing slopes. Arctic tundra, forest-tundra and taiga (boreal forest) covers the rest of the country. I myself have lived in the Yukon Territory for 8 years. So I do know this from personal experience. Several thousand years ago, the climate and plant-cover up there were completely different. Central and northern Alaska and the Yukon were covered then by zonal steppe and forest-steppe.

And on this zonal steppe and forest-steppe, large herds of hoofed animals were grazing, similar to the game herds, roaming now across East Africa’s savannas. Large herds of horses, steppe bison and woolly mammoth were found then "everywhere". They are grazing in the valleys, on the slopes and on the ridges. They were wandering then up to the shores of the Arctic Sea. They were not confined then at all to a few isolated suitable spots, like the feral horse and the introduced bison, living now in central Alaska and the southern Yukon.

Why is that? Why has a zonal steppe or forest-steppe been able to grow then in Alaska and the Yukon? Why is it not growing there now? When would it be able to grow up there again? What would have to change? When would the azonal steppe, covering now only some of the well-drained south-facing slopes and dry basins, change into a zonal steppe, covering most of Alaska and the Yukon? When would this azonal steppe, growing now on some well-drained south-facing slopes, be able to grow also on flat ground as zonal steppe, covering most of the land? – It has to do with the climate. The following findings will help us, to find the answer.

Roger G. Barry is Professor of Geography and Director, WDC-A Glaciology/National Snow and Ice Data Center, at the University of Colorado at Boulder. He states in the book Paleoecology of Beringia (1982:202): "More important to steppe-tundra is Young’s (1976) suggestion regarding the importance of a mosaic of topoclimates. Observational evidence in central Alaska at the present day shows rather small differences in air temperature from north-facing to south-facing slopes, but major contrasts in potential radiation and temperature at the ground surface. Potential radiation estimates on north-facing slopes of about 12° at 65°N in the Yukon-Tanana uplands have an ‘equivalent latitude’ of 80°N, whereas on corresponding south-facing slopes, the equivalent latitude is 50°N (Slaughter and Long, 1975). Surface temperature differences of 4°-7°C were observed in summer 1970 and the mean daily range of surface temperature in June 1971 was 20.6°C on the south-facing slope compared with only 12.1°C on the north-facing slope."

This means: Azonal steppe, growing now only on well-drained south-facing slopes in central Alaska, at 65°N in the Yukon-Tanana uplands, would only be able to change into a zonal steppe, covering also the flat ground, if the warmest month of the year had a mean air temperature of 20.6°C. Zonal steppe would grow there only, if it were just as warm up there, as it is now at 50°N. – That is some 1660 km further south in latitude!

At or close to 50°N in central Asia, near Karaganda, in Kazakhstan, zonal dry steppe is growing now. North of the Caspian and Black Sea, and south of Lake Baikal – also near 50°N -, zonal steppe is growing now. And in North America, near Medicine Hat, southern Alberta, SW Canada, close to 50°N, also zonal steppe (grassland) is found

This proves to me: The zonal Mammoth Steppe was only able to grow in the Far North – near 65°N -, when the climate up there was just as warm, as it is now at 50°N, some 1660 km further south! There is no way around this. This clearly disproves the idea that "periglacial steppe-tundra" was growing near the shores of the Arctic Sea in a severe arctic climate, as we find it now in northeastern Siberia.

How calculated

How warm would it have had to be in summer in central and northern Alaska, so that zonal steppe would also be able to grow there on the flat ground, and not only on a few well-drained south-facing slopes, like today? And where do we find now such a climate? How much further south? - We may calculate the former July temperature of central Alaska at the time, when the woolly mammoth was grazing up there, like this:

The Fairbanks area has now a mean July air temperature of about 17°C (Guthrie, 1982:209). Central Alaska has now a mean July air temperature of 15°C (Bryson and Hare, 1974). The Yukon-Tanana uplands, north of Fairbanks, near 65°N, in June 1971, had a mean ground-surface temperature of 20.6°C on the south-facing slopes, and 12.1°C on the north-facing slopes (R. G. Barry, 1982:202). The flat ground, north of Fairbanks, would have then a mean June ground-surface temperature of 16.35°C (the average of 20.6°C and 12.1°C). Ratio of 20.6° : 16.35° = 1.259938838. I am using now the June value for July, since the ground is warming up there just as soon, or even sooner than in July. The Yukon-Tanana uplands, near 66°N, should have now a July temperature of about 16°C.

16°C x 1.259938838 = 20.6°C.

This means: When the woolly mammoth was living in central Alaska, on a zonal steppe and forest-steppe, growing also on the flat ground, the mean July air temperature had to be then 20.6°C. – At which latitude is this July isotherm of 20.6°C running now? How much further south?

In southwestern Canada, east of the Rocky Mountains, the 20.6°C July isotherm is running now at 48-49°N, at the Canadian-American border. That is some 1900 km further south in latitude. In Eurasia, on the Russian Plain, we do find the 20.6°C July isotherm now at 50-53°N. That is some 1600 km further south in latitude. In Central Siberia, the 20.6°C July isotherm lies now at 50°N, some 1700 km further south. And in East Siberia, the 20.6°C July isotherm lies near 47°N. That is some 2000 km further south in latitude.

In all of these areas, with their mean July air temperature of 20.6°C, at 48-53°N, there is no permafrost and no arctic tundra. There was at least no permafrost closely below the surface. But zonal steppe or forest-steppe is growing there. This proves to me that zonal steppe has only been able to grow in central and northern Alaska, when the mean July air temperature up there has been 20.6°C.

This means: When the woolly mammoth was grazing in the Far North, the climate up there has been just as mild and temperate, as it is now in the zonal steppe of North America and southern Siberia, near 48-53°N. There has been then no permafrost and now arctic winter in Alaska, no arctic tundra, nor any other type of arctic plant-cover. The arctic tundra, forest-tundra and taiga (boreal forest) of North America and northern Eurasia have not existed then. They have come into being much later: in the Holocene Period..