By the time global temperatures approach four degrees above today’s levels, snow will be a rarity at Alpine elevations below 1,000 metres. At 2,000 metres two months will be wiped off the snow season, with the amount of snow accumulating during the winter cut by half. Even as high as 3,000 metres-where snow often lies all the year round in today’s climate-a third of it is expected to melt away…
Even more striking, glaciers will vanish from the majority of even the highest peaks, making the Alps almost completely devoid of ice for the first time in millions of years. Only tiny remnant glacier patches may hang on at the top of the highest 4,000-metre peaks like Monte Rosa and Mont Blanc.
Heatwaves will even hit in the winter months, pushing temperatures up to 20°C between December and February, and melting snow right up in the highest peaks. Plants are tricked by the temperatures into beginning early spring growth, only for buds and tender leaves to be killed off by renewed cold in days and weeks to come….
Indeed it is the sheer temperature rise which begins to dominate over everything else in the four-degree world. Heatwaves of undreamt-of ferocity will scorch the Earth’s surface as the climate becomes hotter than anything humans have experienced before throughout their whole evolutionary history. As we saw earlier, temperatures in Europe will by this time resemble the Middle East more than our more usual temperate climes. The Sahara will have crossed the Strait of Gibraltar and be working its way north into the heart of Spain and Portugal. Even where cultivable soils remain, heavy cloudbursts accelerate erosion, converting once fertile fields into gullied badlands, just like the Texas plains…
Indeed, almost every academic study published about the Paleocene–Eocene Thermal Maximum PETM in recent years mentions that it can be seen as a natural version of whatever human-caused global warming might have in store. One of the first to recognise the importance of the PETM as a ‘natural analogue’ for current greenhouse gas releases was Gerald Dickens, who wrote in Nature as early as 1999 that ‘we can now begin to view aspects of Earth’s future in an entirely new light’. In May 2006, the Harvard University scientists John Higgins and Daniel Schrag reaffirmed this view, stating: ‘The PETM represents one of the best natural analogues in the geologic record to the current rise in atmospheric CO2 due to burning of fossil fuel.’
Although the total carbon input into the atmosphere 55 million years ago was larger than humans have so far managed-with CO2 levels of more than 1,000 parts per million persisting into the early Eocene-the rate of greenhouse gas addition is actually faster now than then. The palaeoceanographer Jim Zachos told the 2006 meeting of the American Association for the Advancement of Science that today’s human carbon emissions are perhaps 30 times faster even than the massive postulated methane belch of the PETM. And judging by carbon isotope ratios in rocks spanning the Palaeocene-Eocene boundary, we are already about halfway to the kind of searing global heatwave that was experienced then by life on Earth.
The likely role of methane hydrates in causing this heatwave also offers another worrying lesson for humanity. Vast amounts of the same methane hydrates still sit, quietly biding their time, on subsea continental shelves around the world. With the oceans now warming up, there is a chance that some of this hydrate will be destabilised and vent catastrophically into the atmosphere in a terrifying echo of the methane belch of 55 million years ago. This would boost atmospheric temperatures further, adding to an unstoppable feedback of runaway global warming. Humans would sit powerless to intervene as their planet began to turn into Venus.
Miriam Katz’s evidence of catastrophic subsea landslides could also offer a grim warning for the future, one where large-scale methane hydrate releases destabilise the sloping ocean bottom and spark similar massive avalanches.
Like shifting tectonic plates, these oceanic landslides can displace huge quantities of water. When this happens, strong shockwaves propagate outwards from the area of disturbance.
And unfortunately, if one of these things happens, the first warning most coastal dwellers have will be towering waves racing towards the shore.