A new temperature reconstruction, using proxy temperature measurements from locations in central Asia, has revealed that there has been no warming in the past 432 years.
by Vijay Jayaraj
The Global Warming “Hiatus” or Pause
The word “hiatus” became popular in recent years after the discovery of a pause or hiatus in global warming. There has been a lack of warming in the atmosphere since 1999, despite the predictions of computer climate models.
The theories that support a hiatus in global warming vary in their conclusions regarding the overall climate scenario. While some forecast that the hiatus will be brief, others say it represents a major shift in our climate system.
Regardless of whether there has been significant shift in the global climate trend, the word “hiatus” implies that there has indeed been a warming trend and that it has stopped—at least momentarily.
That is partly correct, as many well-established scientific studies indicate gradual warming since the end of the Little Ice Age in the 17th century.
It can, however, be declared with absolute certainty that there has been no dangerous warming in the past two decades, and even in the past 200 years. The post-Little Ice Age warming trend has been anything but dangerous, causing hardly any negative impact on the ecosystem or the life forms. Instead, it has brought lengthened growing seasons, more abundant vegetative growth, and more abundant food for people and everything else.
It Is More than Just a Hiatus: Long-term Stability, Followed by Cooling
But more and more studies are beginning to indicate that there has been no significant warming trend in the past five centuries.
Among them is the recent paper by Byambaa et.al., which reveals a lack of warming in Central Asia since 1580 A.D.
The paper used tree ring-width proxy temperature measurements to calculate the mean June‐July air temperatures for the period 1402–2012 and June–December precipitation for the period 1569–2012.
The authors conclude that the past 5 centuries have been relatively cooler. They also find the 20th century to be slightly warmer, but the warming was discontinuous. However, the 20th century warming eventually collapsed due to late 20th century cooling, which they deem common across the mountains of China and Nepal. They also find that solar cycles and volcanic activity were the major reasons for temperature anomalies during the past 5 centuries—not carbon dioxide.
Numerous other studies have attested this recent cooling in Central Asia, especially China. Temperature readings from 118 national weather stations since 1951 in Northeast China reveal a remarkable and significant cooling in China since 1998, the same year since which global atmospheric temperature failed to show any significant warming. Other studies show this trend over all of China.
China is not the only country to experience this late 20th century cooling.
A dozen peer-reviewed scientific papers published during the past three years reveal that the Arctic ceased to warm and the Antarctic began to cool. Other papers report that the 20th century also saw a significant dip in global ocean temperatures.
For example, surface temperatures from Japan have shown no warming trend during the past 50 years and are now beginning to show a cooling trend. And scientists have warned that there might even be a 1-degree Celsius global cooling by the year 2100.
The emergence of these studies has particularly made climate scientists suspect that our climate system’s biggest influencer could be the sun, not greenhouse gases like carbon dioxide.
Hundreds of scientific papers support their intuition and document the natural variations in the climate system owing to the impact of the sun.
The recent cooling, as revealed in the studies mentioned earlier, coincides with the weakest solar cycle on record. The current solar cycle (number 24) is the weakest on record, and scientists have predicted that the next two solar cycles will be much weaker, resulting in more cooling.
In all likelihood, we will experience significant cooling in the coming decade, not a mere hiatus in warming.
Our understanding of the earth’s climate system is still in its infancy. With more and more empirical evidence, it will take us at least a couple of decades to develop a better grasp of how our climate system works.
Vijay Jayaraj (M.Sc., Environmental Science, University of East Anglia, England), Research Associate for Developing Countries for the Cornwall Alliance for the Stewardship of Creation, lives in Bangalore, India.