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It Doesn't Get Any Clearer - Today's Climate Change is Truly Unique

Climate Change

Doubting whether humans are warming up the climate has now really become a rearguard battle. A series of new analyze, published simultaneously in Nature and Nature Geoscience , leaves no room for the argument that climate change is of all times and can therefore have a natural cause. The current warming-up is completely different.  

1. The current warming is really unique

The world is now about a degree warmer than a century and a half ago, and industrial combustion gases are the main cause: science is pretty much in agreement about that. It is less clear how that happened in previous centuries. After all, there were also warm periods in Roman times and the Middle Ages. Only then there were no industrial greenhouse gases.

But look from a distance and from those earlier heat periods little remains. An international consortium of scientists from thirteen universities, with the unusual name of Pages 2K,  analyzed all available climate data  from the last two thousand years. These include direct measurements, but also things that scientists can read about the temperature of the past, such as old sediments, corals, shells, tree rings, antique layers of ice, historical archives and ship logs.

The result is a kind of hockey stick, with a sharp hawk up at the end: the moment, halfway through the last century, when the man-fired greenhouse gasses began to resonate in the climate.
Yes: a hockey stick. In the climate world that is a loaded word, since an earlier hockey stick graph from the nineties turned out to be defective. But the new hockey stick has a handle that goes back a thousand years back to the year zero, and is based on hundreds of the most reliable series of measurements, woven together with seven different statistical techniques.
And, it is no different: 'the clearest warming trend on a time scale of twenty years or longer occurs during the second half of the 20th century',  notes the group  in the journal Nature Geoscience . That makes the warming that we see today 'exceptional' and 'without precedent'.

"That is not new, but it is an important synthesis of what we know," responds climate scientist Wim Hoek (Utrecht University), who is not a participant in the Pages 2K group. 'The picture is actually: for two thousand years not much happened. The Roman warm period and the medieval warm period were only small bumps in the world temperature. Only at the very end of the graph does the temperature really rise. '

2. The warm times of the past were regional

Yes, but wait. There was a time, around the year 1000, when the Vikings founded villages on Greenland and people cultivated wine in England. And under the glaciers sometimes come forests that grew there already in Roman times.

That's right. Only those were always regional heat episodes, according to a  second analysis , published simultaneously in the journal Nature . A Swiss-led group put the climate data of the past two thousand years on the world map and discovered enormous differences.

 For example, the Roman warm period did not reach the rest of the world until five centuries after it began in Europe, and the medieval warmth of the Vikings and British winemakers took place only 40 percent of the globe.
Even the 'small ice age', a cool period between about 1450 and 1850, probably due to the fact that the sun was less active, did not happen everywhere at the same time. Only two centuries after the Dutch masters had immortalized the cold period here in their  famous winter landscapes , did he penetrate Asia and America.
With the current warming that is completely different, the new analyzes show. From the middle of the last century, it strikes everywhere simultaneously, 'unprecedented in spatial consistency', the team solemnly writes. A clear indication that the warming comes from the atmosphere, from all sides at the same time.
"The familiar statement that the climate is always changing is certainly true," says US climate scientist Scott St. George in an accompanying commentary. "But even if we look back to the days of the Roman Empire, we don't find an event that is even somewhat comparable to the warming of the past decades."

3. The models do quite well

Another well-known refrain among climate skeptics: climate models - computer programs that re-enact the climate - are hopelessly wrong.

But here too, the  calculations of the Pages 2K consortium offer  a different picture. The climate models that are currently being used to sketch the future are very successful in imitating the climate of the past. The consortium had the computer re-enact the climate since the year 700, and discovered that the simulation is approaching the real measured world temperature 99.4 to even 99.9 percent accurately.

Only shortly before the year 1300 and just after the year 1800 was the computer a little wrong: the climate models predicted a world of a tenth degree cooler than it was at the time. That is probably because the climate models slightly overestimate the cooling effect of volcanic eruptions  , the team assumes .

In sum, the analyzes provide the image of a planet that is currently taking a whole new climate course, says Hoek. 'If you compare the past with the present, you see something that you actually only see with large climate changes, such as at the end of an ice age. An abrupt blow, all over the world simultaneously. That shows that something is really going on. "

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