This is pretty damning stuff:
Evidence adds up: three studies of human impact on climate. Three new studies were published today, each looking at a different aspect of the human impact on climate, each carrying a sobering message on the consequences of human activities on our environment. The first says recent warming is unprecedented in 2,000 years. A second reports climate zones are shifting faster due to warming temperatures. The third argues impacts from greenhouse gas emissions are not caused solely by warming temperatures.
The one that will likely attract the most attention is a reconstruction of global temperature over the last 2,000 years. This was a mammoth collaboration, involving 78 scientists from 60 scientific institutions, all part of the PAGES network (Past Global Changes). This network enabled researchers to use ice cores, tree-rings, lake sediments and other forms of data from all over the globe. The result – the PAGES 2k Paper – is a robust reconstruction of temperature across seven continents over 2,000 years.
They found that over the last 2,000 years, the planet had been gradually cooling. This cooling trend reversed around the time that humans started emitting heat trapping gases into the atmosphere. Since then, global temperatures have been rising, with the last few decades the warmest in 1,400 years.
If this sounds familiar, it’s because this research is the latest in a long line of papers published over the past 14 years that have consistently found recent warming is unprecedented over the past 1,000 or so years. The seminal paper on global temperature reconstruction was published in 1999 and has attracted much criticism from those averse to the notion of human intervention on climate. However, since that seminal research, a string of papers using different datasets and statistical methods have confirmed the results.
The PAGES 2K paper also found that while the planet as a whole is experiencing unprecedented temperatures in recent decades, some pre-industrial regions were warmer than now. For example, Europe was possibly warmer during the Roman Warm Period. However, different regions warmed at different times. The modern period is the only time that all regions warmed simultaneously.
Another paper published today in Nature Climate Change examined the shifting of climate zones due to warming temperatures. They found that due to warming, climate zones are moving at an increasing pace. If humans continue to emit greenhouse gases at the current rate, the speed with which climate zones are shifting will double by the end of the century. This means about 20% of all land area will undergo a change.