Archive for the ‘Ice Ages’ Category

Climate Change in Context

August 17, 2021

In my last post I showed some plots of temperature data derived from ice cores at Vostok base in Antarctica, which indicate we are close to the end of the Holocene.

Here are some more plots from the same data so we can put present concerns about warming in some context.  Please remember- temperatures calculated from ice cores have a resolution of from 20 years recently to 40 to 50 years in the mid-Holocene, to 80 to 85 years in the glacial maximum.  Temperatures shown may be regarded as a rough average of conditions over those intervals.  Also note this dataset is for one point on the earth’s surface, not a global average.  Nevertheless it is a very important dataset as it shows polar conditions over a very long period.

Figure 1:  Vostok temperatures relative to 1999 over the last 20,000 years

The previous glacial maximum had temperatures in the Antarctic about 9 degrees colder than now.  This was followed by a strong warming, the Termination of glacial conditions, resulting in 11,000 years of warm conditions, the Holocene.  The Holocene was not uniformly warm but featured fluctuations of up to 2 degrees above and below current temperatures.  I will look at this later, but first I shall take a closer look at the Termination.  

Figure 2:  Vostok temperatures during the Termination

Point A marks the start of the Termination warming.  Temperatures rose from A to B (by about 6.5 degrees in 3,000 years- about 0.2 degrees per 100 years- so not exactly “rapid” warming).  Temperatures then fell about 2 degrees, before rising even more sharply from C to D, the start of the Holocene.  Figure 3 shows temperatures in this final part of the Termination.

Figure 3:  Vostok temperatures in the steepest part of the Termination

Temperatures increased by about 5 degrees over a bit more than 1,100 years.  Yes, the warming rate was indeed steeper- 0.44 degrees per 100 years on average.  However, the temperature rose 1 degree in less than 50 years at the end of this period.

During the Termination, long term temperature rise was gradual, but punctuated by short periods of much more rapid rise.

Now let’s look at temperature change in the Holocene.

Figure 4:  Vostok temperatures 7,000 to 9,000 years ago

Conditions were not uniformly warm, with fluctuations from -1 to +.5C relative to 1999 over hundreds of years.  But there was one episode with a rise of 2.93 degrees in less than 100 years- now that’s rapid warming.

Figure 5:  Vostok temperatures in the last 2,020 years

More recently, temperatures rose 1.94 degrees in 155 years to 1602, and again 2.2 degrees in 44 years to 1809.

You will notice I have shown 3 datapoints showing 21 year mean annual surface air temperatures at Vostok (1970, 1990, and 2010, with zero at 1990).  This is merely for interest- instrumental air temperatures should never be appended to ice core data.  What it does show is that the rate of present temperature change is well within the range of natural variation.

This is also evident when a Greenland ice core series is compared with modern surface air temperatures.

Figure 6:  Greenland (GISP2) temperatures in the last 4,000 years

I have inserted the decadal average of -29.9 C at the GISP borehole from 2001-2010.  Notice how unremarkable that is.

As the fluctuations at GISP and Vostok have been occurring for thousands of years something other than carbon dioxide emissions must be responsible.

So what about carbon dioxide? Data in the next figure is from Dome Fuji, also in Antarctica.

Figure 7:  Insolation, temperature, and CO2 in the last 350,000 years

Notice that at no time in previous interglacials did carbon dioxide concentration exceed 300ppm, (and despite the higher temperatures than now there was no “runaway” warming.)    And as the Carbon Dioxide Information Analysis Centre says

There is a close correlation between Antarctic temperature and atmospheric concentrations of CO2 (Barnola et al. 1987). The extension of the Vostok CO2 record shows that the main trends of CO2 are similar for each glacial cycle. Major transitions from the lowest to the highest values are associated with glacial-interglacial transitions. During these transitions, the atmospheric concentrations of CO2 rises from 180 to 280-300 ppmv (Petit et al. 1999). The extension of the Vostok CO2 record shows the present-day levels of CO2 are unprecedented during the past 420 kyr. Pre-industrial Holocene levels (~280 ppmv) are found during all interglacials, with the highest values (~300 ppmv) found approximately 323 kyr BP. When the Vostok ice core data were compared with other ice core data (Delmas et al. 1980; Neftel et al. 1982) for the past 30,000 – 40,000 years, good agreement was found between the records: all show low CO2 values [~200 parts per million by volume (ppmv)] during the Last Glacial Maximum and increased atmospheric CO2 concentrations associated with the glacial-Holocene transition. According to Barnola et al. (1991) and Petit et al. (1999) these measurements indicate that, at the beginning of the deglaciations, the CO2 increase either was in phase or lagged by less than ~1000 years with respect to the Antarctic temperature, whereas it clearly lagged behind the temperature at the onset of the glaciations. (My emphasis).

Therefore, carbon dioxide did not drive, but followed, temperature change in the past; past rapid warming did not lead to positive feedbacks and runaway warming; and the instrumental record is far too short to draw any definitive conclusion about recent warming, which cannot be differentiated from past Antarctic and Greenland temperature fluctuations.

There is no climate crisis.

Global Warming or Global Cooling: Keep an Eye on Greenland

July 30, 2021

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.