Earth warming for more than 1,000 years

Three new climate studies published by different groups of researchers in refereed journals have provided a grim view of the future facing Earth and its inhabitants.

The first involved a massive collaboration between 78 scientists from 60 institutions that are part of the Past Global Changes or PAGES network.

In a paper published in Nature Geoscience, the researchers reconstructed global temperatures over the past 1,000- to 2,000 years for seven ‘continental scale’ regions using ice cores, tree-rings, lake sediments and other forms of data from across the globe.

They found that although Earth had been gradually cooling over millennia, the cooling trend reversed around the time humans started emitting heat-trapping gases into the atmosphere. Since then, global temperatures have been rising, with the past few decades being the warmest in 1,400 years.

Reporting on the findings of this and the other two studies, Dr John Cook, a climate communication fellow at the University of Queensland, said the research findings were the latest in a long line of papers published over the past 14 years that have consistently found recent warming is unprecedented.

Writing in The Conversation, Cook noted that the latest paper showed that while the planet as a whole had experienced unprecedented temperature rises in recent decades, some pre-industrial regions were warmer than now.

Europe was possibly warmer during the Roman Warm Period, but while different regions used to warm at different times, the modern period is the only one when all regions have warmed simultaneously.

In a second paper, published in Nature Climate Change, researchers examined a shifting of climate zones because of warming temperatures.

They said warming climate zones were moving at an increasing pace and, if humans continued to emit greenhouse gases at the current rate, the speed would double by the end of the century. This meant that about 20% of all land area on the planet would face serious changes.

Shifting climate zones are already causing thousands of animal species to move towards higher latitudes and higher altitudes to remain within a tolerable temperature range, Cook said. The shift would also affect agriculture as a result of precipitation patterns changing with the shifting climate zones.

He said that one suggested ‘magic bullet’ to minimise the impacts of human-caused global warming was geo-engineering, such as putting tiny sulphate particles into the atmosphere that could reflect incoming sunlight and cool the planet.

But the third study, also published in Nature Geoscience, reported that some impacts from greenhouse gas emissions could not be fully mitigated by geo-engineering.

The researchers simulated ‘business-as-usual greenhouse gas emissions’ over the 21st century and found that many of the changes in regional rainfall were not related to surface warming. Instead, the extra carbon dioxide in the atmosphere was causing shifts in atmospheric vertical motions, which led to changes in tropical rainfall.

“This means that even if geo-engineering managed to cancel out surface warming, rainfall patterns would still change because of the extra carbon dioxide building up in the atmosphere,” Cook said.

“There are other consequences of the increased carbon dioxide, beyond surface warming. For example, the oceans are absorbing around half of our carbon emissions, which is having a negative impact on coral reefs because of ocean acidification.”

Research into the impacts of human-caused global warming continues to mount, he said. A Web of Science search for papers matching the terms ‘global climate change’ or ‘global warming’ found an accelerating amount of climate research.

This increasing body of evidence only served to strengthen the scientific consensus that formed as long ago as the early 1990s. So why, he asked, is the general public still confused about climate change, lagging behind the scientific community by two decades?

Cook pointed out that despite the steady accumulation of studies documenting the human impact on climate change, misinformation disseminated by a small number of climate ‘misinformers’ has had an impact on public attitudes.

“In my own research, I measured the public perception of scientific consensus by asking a representative US sample how many scientists agree that humans are causing global warming. The average answer was a shade under 50%.

“This is in stark contrast to two recent studies that independently found a 97% consensus – a ‘consensus gap’ that has policy implications because when the general public correctly perceive the scientific consensus, they are more likely to support policies to mitigate greenhouse gas emissions.

“As more research like in the latest papers is published, we can expect climate misinformers to continue to deny the full body of evidence. Inconvenient studies will be attacked and data will be cherry picked.

“The public needs to understand that on a fundamental topic such as human-caused global warming, the attacks don’t come from genuine scientific debate but an attempt to generate false controversy.”