This week and next, Discovery Earth is focusing on the science of climate change. To that end, to help clarify some of the misunderstandings and misrepresentations of a number of climate change issues, we will be looking at a selection of the more common myths and questions surrounding global warming.
The topics tackled in this series by no means provide a comprehensive list; for such a list, I thoroughly recommend repeated visits to Skeptical Science, which addresses a great many more climate myths than we have room for here. Other excellent outlets include RealClimate and Climate Progress; and New Scientist magazine also compiles an ongoing and regularly updated "guide for the perplexed."
Each of the entries in this particular blog are, through necessity
induced by the requirement for brevity, mere thumbnails; each contains
links to background information that paints a broader picture.
Parts II and III of the series will appear on Wednesday and Friday, respectively.
Polar bears are increasing in numbers.
However, despite her cavalierly and irresponsibly repeating the claim
as if it were established fact, it is in fact complete fiction. Not a
single polar bear biologist would tell you that polar bear numbers have
doubled in the last few decades, any more than they would tell you they
have halved. In the 1960s, early guesses – and they were indeed guesses
- of polar bear numbers worldwide ranged from 5,000 to approximately
20,000, the latter of which is roughly the accepted figure today.
Former CNN producer Peter Dykstra did a very good job of highlighting the lack of a sound basis (or even an identifiable source) for the "polar bear numbers have mutliplied" assertion.
The key concern for polar bears is of course the fact that their fate is tied inextricably to the sea ice of the Arctic Ocean, which, in thickness and extent, is undergoing a steady decline. Accordingly, the IUCN Polar Bear Specialist Group estimates that, of 19 recognized subpopulations of polar bears, one is currently increasing, three are stable and eight are
declining. (For the remaining 7 subpopulations available data were
insufficient to provide an assessment of current trend). This status table provides the most accurate information on the status and trends of polar bear populations worldwide as of 2005.
We are in a period of global cooling.
Another very common comment, and equally easy to address – as indeed we have done several times, for example here and here. It stems from an oft-stated assertion that, since 1998, warming has flatlined or even declined. But such apparent non-warming is, as this study showed, a statistical quirk caused by taking as a starting point the anomalously warm year of 1998; start with 1997 or 1999, and the perceived flatlining disappears. It also disappears if, instead of using data from the Hadley Center for Climate Protection and Research, which considers 1998 to have been the warmest year on record, you use figures from NASA's Goddard Institute for Space Studies, which awards that honor to 2005. Both NASA and the World Meteorological Organization have confirmed that the period 2000-2009 looks set to be the warmest decade on record.
(Irony alert: deniers are perfectly happy to embrace Hadley/Climate
Research Unit data when they can use it to infer global cooling, but
reject those institutions and their data out of hand in all other
respects, particularly following the release of highly selective
excerpts of a handful of e-mails, about which more later).
It is worth pointing out that the reason for the difference between the Hadley and NASA interpretations is that the latter is a much more complete record; because the former does not cover the entire globe and misses regions where warming has been most pronounced (specifically, the Arctic), it underestimates warming in recent years.
The "hockey stick" has been discredited.
Skeptics/deniers like to claim that the famed "hockey stick" graph -
which shows a lengthy period of essentially stable temperatures over a
period of several centuries, followed by an upward surge beginning in
the latter part of the twentieth century – has been "debunked." Much of
this claim rests on an analysis by Canadian skeptics Stephen McIntyre and Ross McKitrick, who claimed that the original hockey stick reconstruction, by Michael Mann, Raymond Bradley and Michael Hughes, was an artifact of flawed calculations and serious data defects. However, these authors and others rebutted those claims, several other analyses have produced similar representations, and a 2006 review by the National Academy of Sciences "broadly
endorsed conclusion that Northern Hemisphere temperatures in the
late 20th Century were probably warmer than at any time in the previous
400 years, and perhaps at any time during the previous 1,000 years," as
The NAS study did encourage researchers to use a greater number and
variety of proxy records (i.e. tree rings, ice cores, growth patterns
of coral etc), and in 2008, the original three authors, and others,
responded with a paper that did just that.
Far from eliminating the hockey stick, this effort lengthened the
handle, showing that "recent warmth appears anomalous for at least the
past 1,300 years."
Claims of recent human-induced warming ignore the Medieval Warm Period and the Little Ice Age
There are two parts to this. One claim, which is strongly related to
the hockey stick controversy, is that temperatures were as warm as, or
warmer than, they are today during the so-called Medieval Warm Period;
the other is that measurements suggesting recent warming are misleading
because the mid-nineteenth century saw the planet emerging from the "Little Ice Age"
that succeeded the Medieval Warm Period. Generally speaking, the
Medieval Warm Period (MWP) is claimed to have lasted from approximately
800 to 1300 CE, and the Little Ice Age (LIA) from roughly 1450 to 1850.
However, as this study among
others has pointed out, while there are indeed indications of warming
during the former period and cooling during the latter, these changes
appear to have been regional, rather than global, in nature, and to
have been sporadic rather than continuous. Specifically, evidence of
both the MWP and LIA comes primarily from North Atlantic area records;
albeit admittedly from a lesser amount of data, Southern Hemisphere
records paint a more mixed, and in some cases contradictory, picture.
Additionally, some of the historical evidence cited in favor of both
episodes may have been skewed by other factors: For example, it is
frequently stated that the River Thames would freeze over every year
during the LIA, but records indicate it did so only 22 times between 1408 and 1714, and that this freezing may have been at least partly due to the way the old London Bridge constricted river flow.
Importantly, even under those reconstructions that include a MWP,
temperatures in the late 20th century have been warmer than at any time
during the medieval period. Additionally, even during warm and cold
periods, average temperatures for much of the past 1,300 or so years
appear to have been within a "sweet spot" spanning approximately 1
degree Celsius; we are now climbing out of that band and are predicted to climb far farther in the coming century.
In the 1970s, scientists were warning about a new Ice Age, so why should we trust them now?
Some scientists were speculating in the 1970s about the prospect of a rapid cooling,
and with good reason. The previous few decades had indeed experienced a
cooling (probably as a result of particulates in the atmosphere, a
combination of pollution and a series of volcanic eruptions) and
studies suggested Earth was experiencing an atypically long
"interglacial" period – it has been 10,000 years since the most recent
Ice Age, whereas the previous interval between Ice Ages had been 5,000
years. Plus there was a growing realization, based on the first
Greenland ice cores, that climate could change rapidly.
But much of the frenzy was in the popular media, not the peer-reviewed scientific literature. A young researcher called Stephen Schneider
played a large part in setting the ball in motion with a paper in 1971
that concluded the cooling effect of aerosols would exceed the warming
effect of greenhouse gases; three years later, he published a
correction that stated that the balance in fact tipped strongly toward
warming. In 1977, he criticized a popular book that predicted an
imminent ice age, and is today one of the most articulate and influential scientific commentators on global warming.
(opens PDF) demonstrated categorically that the "global cooling
consensus" is a myth. Of 71 scientific studies of future climate that
they found in the peer-reviewed literature between 1965 and 1979, 20
were neutral and 44 predicted greater warming. Just seven predicted a
new era of cooling.