Climatologists were wrong: the planet is warming twice as fast as expected.

An international team of 59 scientists from 17 nations has just published a report in the journal Nature Geosciences. Their observation is terrible: global warming could be twice as much as climate models predict. These are amplification mechanisms, poorly represented in the models, which increase warming and its effects on the planet. On the agenda: a 6-metre rise in the level of the oceans, the greening of the Sahara, the drying up and burning of Mediterranean areas, the transformation of tropical zones into arid savannahs, among others.

 

Ahe results published last week in Nature Geoscience are based on observational data from three warm periods over the past 3.5 million years, when the world was 0.5°C-2°C warmer than the pre-industrial temperatures of the 19th century.

To obtain their results, researchers looked at three of the best documented warm periods, the Holocene thermal maximum (5000-9000 years ago), the last interglacial age (129,000-116,000 years ago) and the mid-Pliocene warm period (3.3-3 million years ago).

 

The warming of the first two periods was caused by predictable changes in the Earth's orbit, while the mid-Pliocene event was the result of atmospheric carbon dioxide concentrations that were 350-450 ppm - about the same as today.

 

By combining a wide range of measurements from ice cores, sediment layers, fossil records, atomic isotope dating, and a host of other established paleoclimatic methods, researchers have reconstructed the impact of these climate changes.

 

Taken together, these periods clearly show how a warmer Earth would appear once the climate has stabilized. The problem is that today, our planet is warming much faster than any of these periods, as human emissions of carbon dioxide continue to rise. Even if our emissions stopped today, it would take centuries to millennia to reach equilibrium.

 

The changes on Earth under these past conditions have been profound - there has been a substantial retreat of the Antarctic and Greenland ice sheets and, as a result, sea levels have risen by at least six metres; marine plankton chains have altered the reorganization of the entire marine ecosystem ; the Sahara has become greener and forest species have moved 200 km towards the poles, such as the tundra; high-altitude species have declined, temperate tropical forests have been reduced and, in Mediterranean areas, landscapes with fire-damaged vegetation have dominated.

 

Evidence collected in the past suggests that even with global warming limited to 2 degrees Celsius above pre-industrial levels, as set out in the Paris Agreement, climate zones and ecosystems will shift, rapid polar warming may release additional greenhouse gases, and sea levels will rise by several metres. These observations show that many current climate models designed to predict changes this century underestimate longer-term changes.

" Even with only 2°C of warming - and potentially only 1.5°C - the significant impacts on the earth system are profound. "said Professor Alan Mix, co-author at Oregon State University.

 

Ecosystems and climatic zones will generally move towards the poles or to higher altitudes. This is already the case with scientists' observations of plant species fleeing in numbers from warm zones to migrate to higher altitudes or latitudes.

In response, thawing permafrost can release more carbon dioxide and methane into the atmosphere, causing further warming. Past observations suggest that if warming can be limited to a maximum of 2 degrees Celsius as proposed in the Paris Accords, the risk of catastrophic greenhouse gas feedback is relatively low. Nevertheless, the significant amount of additional carbon dioxide released from permafrost and soils must be factored into future emissions budgets.

" Accounting for additional CO2 emissions leaves even less room for error as humanity seeks to reduce its CO2 emissions and stabilise the global climate within reasonable limits. "said Hubertus Fischer of the University of Berne.

 

Nevertheless, a warming of 1.5 to 2 degrees Celsius above pre-industrial levels will be sufficient to trigger substantial long-term melting of the ice in Greenland and Antarctica and a sea level rise of more than 6 metres. Higher rates of sea level rise than in recent decades are likely. Professor Alan Mix stressed the importance of this sea-level rise by saying: "... the sea level is likely to rise at rates greater than those of recent decades. We are already starting to see the effects of rising sea levels. This rise could become unstoppable for millennia, impacting much of the world's population, infrastructure and economic activity that is close to the coast. ".

Yet these observed significant changes are generally underestimated in climate model projections that focus on the short term. Compared to these past observations, climate models appear to underestimate long-term warming and heat amplification in the polar regions. « Climate models appear to be trustworthy for small changes, such as scenarios of low emissions over short periods of time, say over the next few decades to 2100. But as the change amplifies or becomes more persistent, either because emissions are higher, for example in the business-as-usual scenario, or because we are interested in the long-term response of a low-emissions scenario, they appear to underestimate climate change. "said Professor Katrin Meissner, co-author and Director of the Climate Change Research Centre at the University of New South Wales.

 

According to the researchers, this information from the past underscores the urgency of reducing carbon dioxide emissions in order to meet the Paris Accords in this century and beyond. The authors warn: " This research is a powerful call to action. It tells us that if today's leaders do not urgently address our emissions, global warming will bring profound changes to our planet and our way of life - not just this century, but far beyond. ".

 

Researchers cannot give a timeline of the current change and the coming disaster. But each one of us can observe, in his or her own way, that changes are taking hold in our daily lives, that they are accelerating and that many unusual events (heat waves, floods, storms, droughts, fires...) are becoming more and more routine. Climate change is here to stay, and it looks like it will be here for a long time. Returning to a previous situation seems illusory. Containing the damage and trying to adapt is possible. Is it in the order of the probable?

 

 

Source: phys.org