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Extreme Weather Events: Are they Influenced by Rising Atmospheric CO2?

1. Introduction

The lexicon used to describe and frame the public debate over the potential impacts of rising carbon dioxide (CO2) emissions on Earth's climate and biosphere has changed over the years from global warming to climate change to extreme weather. Such phrases, however, are woefully simplistic in their ability to accurately portray and capture the multitude of complexities, intricacies, and nuances associated with a multifaceted subject that spans several academic disciplines, yet they have been effectively used to communicate a desired message and to shape both public opinion and policy.

The term "global warming" originated from computer model studies conducted over three decades ago that projected rising atmospheric CO2 concentrations would alter important energy transfer processes in the Earth-ocean-atmosphere system and cause a significant warming of the globe that would lead to a host of other environmental changes, including the melting of substantial portions of the polar ice caps, rising sea levels, super-hurricanes, and devastating floods and droughts. Because rising temperatures were often predicted to cause changes in these and other environmental variables, "global warming" became the generic term to describe all resultant impacts that might arise from an increase in CO2. Those who accept this "global warming" hypothesis are known as climate alarmists because they are alarmed about these potential impacts. Those who challenge it are referred to as climate skeptics.

Public acceptance and use of the phrase "global warming" could not have pleased the climate alarmists more, for it effectively reduced the battle of public opinion and policy debate of an incredibly complex subject to just one parameter-temperature. And because the average person has very limited knowledge of the physics and processes that influence climate, it was relatively easy for a large portion of the public to assume that they could evaluate and judge the merits of the very complex global warming debate by the sole measure of global temperature. And with the temperature record showing a marked increase since the mid-1970s, it was a fairly simple leap for many individuals (including a number of scientists) to accept the hypothesis that the late 20th century rise in temperature was caused by rising atmospheric CO2 and that all the model-based projections associated with global warming were likely true.

By the early 21st century, however, observations from satellite data made it clear that global temperatures had plateaued, despite increasing emissions of CO2 into the atmosphere. As a result, public support for policy initiatives to combat global warming began to wane. In an effort to avert this slide in public opinion, climate alarmists began to supplant their use of the phrase global warming with the new axiom of climate change.

Shifting public conversation away from global warming toward climate change was an important tactical move, as it allowed climate alarmists the opportunity to expand their narrative beyond temperature. Up until this time, in claiming the modern rise in CO2 was the cause of modern global warming, climate alarmists had effectively limited "proof" of their thesis to the global temperature record for an unsuspecting and largely uneducated public on this topic. It was a brilliant strategy that worked flawlessly when global temperatures cooperated and rose during the 1980s and 90s, but it failed miserably when temperatures plateaued in the new millennium.

One of the most damning arguments put forth at that time against global warming alarmism was a graph of temperature projections derived from climate models that were plotted alongside real-world observations. As shown in Figure 1, this plot reveals a growing divergence between the two as time proceeds. This illustration resonated well with a large portion of the public who began to question in larger and larger numbers how the climate alarmist thesis could be correct if the singular measure by which they had been preconditioned to judge it by, i.e. global temperature, failed to rise in the manner predicted by the models? Simply put, it couldn't be right; and opinion polls began to show the public abandoning their support of the climate alarmist position in droves. Thus, a new narrative had to emerge if the global warming hypothesis was to survive this challenge. And so there was another shift where "global warming" was replaced with "climate change." However, there would still be a challenge in getting the public to accept this new lexis and revert back to supporting the climate alarmist position. And fortunately for them, there was a near endless supply of politicians and members of the media who were all too anxious to promote the word switch ... and make it stick.

Figure 1. Mid-tropospheric (MT) temperature variations for the tropics (20°N to 20°S) in 73 current (CMIP5) climate models versus measurements from two satellite datasets and four weather balloon datasets. From Spencer (2013).

Replacing public expression of the term "global warming" with "climate change" provided climate alarmists with two important advantages in the battle with climate skeptics over public opinion. First, the new phrase now allowed them wiggle room if temperatures failed to rise or even cooled. Previously, under global warming, if temperatures plateaued or fell the jig was up. With climate change it no longer mattered if temperature observations failed to match model projections. Regardless of whether global temperatures warmed or cooled, the new terminology implied that rising CO2 could be the cause of both!

A second important advantage was that the new phrase allowed climate alarmists the opportunity to expand their narrative with the public beyond temperature. Now, other measures of climate could be trumpeted and heralded before the public as additional proofs of so-called "climate change." It allowed them to take a parameter such as Arctic ice volume, for example, and claim something like "its downward trend over the past three decades is clear evidence of climate change." As explicitly presented, the statement above is correct. Even climate skeptics would be forced to admit as much. Sea ice volume in the Arctic has indeed declined in recent years as a result of some change in climate. However, the statement is also grossly misleading, for it says nothing about the cause of the sea ice decline. The decline in Arctic sea ice could be caused by CO2-induced global warming, but it could just as well be caused by natural warming, or by changes in ocean or atmospheric circulation, winds, precipitation, albedo, or other factors, many of which can and do change naturally and independently of the air's CO2 content. It is thus disingenuous to intimate that CO2 is driving a change in a particular climatic parameter without explicitly stating so or providing any real-world proof. Nevertheless, climate alarmists have been waging such a campaign and they have been quite successful in cajoling the public to accept the premise that any climate change during the modern era is largely the consequence of the concomitant rise in atmospheric CO2. And success on this front has emboldened them to take the more recent and controversial leap of linking extreme weather events with rising CO2.

Turing the debate toward extreme weather events provides an additional advantage of playing on the public's short-term memory, for hardly a day goes by in which there is not some extreme weather event causing some sort of danger or damage somewhere on the planet. Thus, there exists a near-endless supply of opportunity for climate alarmists to promote their message on a regular basis. Hurricane Sandy is a good example. When it struck the U.S. Atlantic seaboard in the fall of 2012, notwithstanding evidence from numerous scientific studies that demonstrate there has been no observable increase in Atlantic hurricane frequency or intensity over the past few decades, various media, politicians and scientists were quick to claim the hurricane was caused by rising greenhouse gases in the atmosphere. Others were slightly more reserved. Although not willing to go so far as to assert Sandy was caused by CO2-induced global warming/climate change, they promoted the alarmist narrative and rhetoric by asserting more such storms could be expected in the future if CO2 emissions continue to rise.

Nowadays, hardly any extreme weather event passes without someone somewhere claiming it was either caused or made worse by rising CO2; and it is shortly followed by demands for regulatory action to reduce CO2 so as to avoid such occurrences in the future. These petitions nearly always reach the ears of United States Environmental Protection Agency, who in June of this year unveiled a Clean Power Plan aimed at reducing emissions of carbon dioxide from the nation's power sector by 30% (relative to 2005 levels) by the year 2030. One of the primary reasons for justifying this action was their stated concern that rising CO2 will increase the frequency and severity of extreme weather events.

Yet, for all their brilliance in shifting the public's focus on this issue from global warming to climate change, climate alarmists made a tactical mistake in moving the battlefront to extreme weather.

The only way to test the model projections of CO2-induced climate change is to wait a sufficient period of time before the projections can be compared with observations. Because climate, by definition, is the long-term average of day-to-day weather fluctuations, literally decades can be required before enough observations are collected to enable a proper evaluation of the model projections. This allows climate alarmists a period of years to decades in which they can actively promote their claims without ever being held accountable by observations. The tactical mistake they made in claiming that rising CO2 will increase the frequency and severity of extreme weather events, however, is that they can be held accountable for this assertion now; for empirical analyses can be readily performed to test the correctness of this thesis by examining how extreme weather events have changed (or not changed) in response to the approximate 40% rise in atmospheric CO2 since the Industrial Revolution.

The present work conducts just such an analysis, examining trends in extreme weather events over the historical past using instrumental observations and paleoclimate proxies. It is prefaced by a discussion of three fundamental principles that must be followed in order to properly deduce a scientific link between rising CO2 and extreme weather, principles that climate alarmists consistently ignore in their attribution of recent extreme weather events to CO2-induced climate change. Thereafter, the work provides a detailed analysis of trends in three key categories of extreme weather events, floods, droughts, and storms, finding no compelling evidence to support the claim of a CO2-indcuded influence on these extreme weather events. Scientific analysis and observation prove otherwise. Claims that global warming or climate change are causing or will cause an increase in these key extreme weather occurrences, therefore, amount to nothing more than a deceitful public relations ploy designed to confuse and scare the public into supporting regulatory actions aimed at reducing CO2 emissions. Rising atmospheric carbon dioxide is not making extreme weather worse and reducing the air's CO2 content will not cause the frequency or intensity of such events to diminish.

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