What is it about the hottest decade in recorded history that’s so hard to understand?
The first decade of this millennium ― 2001 to 2010 ― was the warmest since measurements began 160 years ago. The earlier hottest decade was during the 1990s. And the record-breaker before that? The 1980s. These are undisputed facts.
Nothing about this steady rise suggests our planet is doing anything but warming. Yet some people who have long resisted the consistency of this trend are now saying that climate change has “paused.” In doing so, they ignore the longer trend, miss the big picture, and distort the public conversation about the strength of the evidence for climate change.
The new report from the Intergovernmental Panel on Climate Change was explicit and voluminously documented on this point: climate change is happening now, and if we do not reduce greenhouse gas emissions, future climate disruption will be very costly.
As an ocean scientist and a veteran of former IPCC and other climate assessments, I have seen the scientific evidence for climate change become increasingly solid. Science rarely gets more clear than this.
Here is some additional certainty. These are simple facts, based upon meticulous measurements and published in peer-reviewed journals:
― Arctic sea ice? The last seven years have been the lowest recorded in more than three decades of satellite observations.
― Rising sea level? The rate of rise was almost twice as fast over the past 20 years than earlier in the 20th century.
― Fingerprint of humankind? Warming is continuing, despite the fact that in the last decade there were two cooling La Ninas in the Pacific Ocean and a prolonged solar minimum.
These and other indicators of change all signal that human activities, such as the release of greenhouse gases, are changing our climate ― a conclusion that 97 percent of climate scientists agree with in a recent peer-reviewed study.
Further delay in addressing climate change will make it more difficult and more costly to avoid or counter the impacts of a disruptive climate.
If anyone should see the big picture clearly, it should be those in the financial community. Readers understand that growth is not necessarily uniform on all time scales ― the S&P 500 grew in value by 2400 percent from 1975 to today. No one disputes this, even though an investor at the peak in 2000 would have seen no real gains until 2013. During that “pause,” sometimes called the Lost Decade, investors weren’t all saying that economic growth had stopped for all time and that further investment in stocks was futile.
Those who are arguing that climate change has paused use 1998 as a starting point for their short-term glimpse at climate change. This is like using the year 2000 as the basis for an investment scenario. It puts undue weight on a year with perhaps the strongest El Nino warming event in a century. Subsequently, only 2005 and 2010 were a bit warmer, with the latter helped by a moderate El Nino.
Moreover, it is important to keep in mind that the data attracting the most attention from those who would minimize the findings of climate science are only surface temperatures of the globe. The ocean covers 70 percent of our planet, and its depths now hold more than 90 percent of the extra heat that has been absorbed, due to humanity’s greenhouse gas emissions. Data show that the ocean has warmed to 6,000 foot depths in many regions ― an observation that as a graduate student working in the north Pacific decades ago, I could not have imagined possible within my lifetime.
Climate scientists increasingly express concern about abrupt changes that could occur as thresholds are crossed, with even faster melting of ice caps and release of methane from permafrost. There is tremendous financial risk inherent in unabated climate change, a risk that the World Bank puts at $1 trillion a year.
These concerns should further inspire all of us, for the sake of future generations, to explore and agree upon solutions that slow the rate of climate change and prepare for the change that cannot be avoided. Indeed, that was the point when the IPCC was created in 1988: to provide policymakers with the clearest summary of the scientific consensus, so they can debate the most effective policy instruments to reduce the rate of climate change.
Earth’s climate is changing in profoundly unusual ways. We are wittingly and unwittingly contributing to this change. The evidence couldn’t be more clear. Perhaps the largest uncertainty about future climate is whether or not we as a people will engage the power of scientific understanding to reduce the chances of major climate disruption.
James J. McCarthy is professor of biological oceanography at Harvard University. Readers may send him email at jmccarthy@oeb.harvard.edu. ― Ed.
