In our last World Climate Report article, we described new findings that verified older findings that the patterns of sea surface temperature (SST) variations in the Atlantic Ocean (including in the tropical Atlantic region which is the birthplace of Atlantic tropical storms and hurricanes), are largely a reflection of natural variability, with some anthropogenic warming thrown in for good measure.

This time, we report on new research that finds that rather than a large dose of anthropogenic warming, a decline in the amount of dust coming off of the Saharan desert may have collaborated with multidecadal natural oscillations to produce the observed warming trend in Atlantic tropical SST over recent decades. An implication of this finding is to further lessen any impact than human emissions of greenhouse gases may have had on the observed behavior of Atlantic hurricanes, including the recent upturn in activity.

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There is a degree of disagreement among climate scientists as to whether or not a phenomenon known as the Atlantic Multidecadal Oscillation (AMO) is a true physical mechanism operating in the Atlantic Ocean (e.g., Delworth and Mann, 2000; Knight et al., 2005; Zhang, 2007), or whether it is largely a manifestation of the pattern of the anthropogenic influence on the earth’s climate (Mann and Emanuel, 2006). The subject is of considerable interest in that many researchers have identified other climate phenomenon that seem to be related to the patterns of the AMO—primary among which are the patterns of Atlantic hurricane activity (e.g. Goldenberg et al., 2001). Thus, the source of the AMO likely sheds light on the source of Atlantic hurricane frequency and intensity fluctuations—are they primarily natural in origin, or are they primarily caused by human emissions of greenhouse gases and aerosols?

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We are sure many of you remember headlines similar to these: “Global Warming to Cause Next Ice Age!” or “Global Warming to Send Europe into a Deep Freeze!” In fact, next time New England or Europe has a cold winter, we’ll guarantee that you’ll see them again. The idea behind this scare story (and the premise of the climatefright film The Day After Tomorrow) is that the ocean’s thermohaline circulation (which among other things modestly warms the winter climate of western Europe) slows down, or even worse stops, sending the climate into disarray—all because of anthropogenic global warming. In the case of The Day After Tomorrow, this circulation shut down led to a flash freeze of the planet, while more “reasonable” climate alarmists at least give it a couple of decades to turn Europe into the icebox. But, in reality, things just don’t seem to be headed that way at all.

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What’s the first image that comes to mind when you hear the term “global warming”? The most common is that of melting ice. That image is then easily cultivated by climate change alarmists who would like you to translate it into a downward spiraling Arctic ecosystem and a sputtering global oceanic circulation. (The image that comes to our mind is that of Al Gore recently pretending to be a research professor on The Oprah Winfrey Show.) What we hear little about from the global warming crusade is research findings that suggest that a measure of the recent atmospheric warming is part of a natural cycle or that the impacts are far less than what is portrayed. Well, that’s what we at the World Climate Report are here for.

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“False Alarm: Atlantic Conveyor Belt Hasn’t Slowed Down After All” is the title of a “News of the Week” piece in this week’s (November 17, 2006) Science magazine by science writer Richard Kerr (for those with a subscription, you can view the whole story, here).

Kerr’s piece starts off with the line “A closer look at the Atlantic Ocean’s currents has confirmed what many oceanographers suspected all along: There’s no sign that the ocean’s heat-laden ‘conveyor’ is slowing.”

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As the very quiet hurricane season of 2006 comes to an end, two very interesting articles have appeared in the peer-reviewed scientific journals on the subject of climate change and hurricane activity. In the most recent issue of the Bulletin of the American Meteorological Society, Philip Klotzbach and William Gray of Colorado State University analyzed the causes of the destructive 2004 hurricane season. In case you have forgotten, Katrina and a number of other large hurricanes were part of the 2005 hurricane season. The 2004 season was also very active, but nearly forgotten given the events of 2005.

Klotzbach and Gray began their article by noting “In the aftermath of the destructive 2004 hurricane season, many individuals queried whether the landfall of four destructive hurricanes in such a short period of time was related to human-induced climate change brought on by increased greenhouse gas emissions. The Center for Health and Global Environment at the Harvard Medical School held a news conference in the wake of the four storms and indicated that humans were likely to be somewhat responsible for these damaging cyclones.” A year before Katrina and 2005, the drums of the global warmers were already beating out their message that hurricanes should be blamed on fossil fuel emissions and the resulting increase in planetary temperature. Gore and others make this theme a centerpiece in their disinformation campaign.

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The Arctic region has become a bit of an epicenter of the global warming debate. Snow and ice cover are touted as effective monitors of large-scale climate change, the greatest warming in recent decades is said to have occurred over portions of the Arctic, and climate models predict that the region will experience some of the most significant warming in the future. Throw-in the idea that melting snow and ice increases the input of fresh water to the Arctic and northern Atlantic Oceans, which alters the oceanic thermohaline circulation, which changes the global climate further, and you can understand why the global warming crusade gets dreamy-eyed when thinking of the cold northern latitudes. The truth of the matter is that there have been many contradictions to the doomsday scenarios associated with the Arctic region – enough to champion a movie sequel “Day After Tomorrow 2: Hold the Phone!”

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You may remember a major study regarding the greenhouse debate that surfaced last Christmas season. Harry Bryden and two associates at the UK’s National Oceanography Centre had analyzed five decades of data regarding the ocean circulation of the North Atlantic. They concluded in Nature magazine that “The comparison suggests that the Atlantic meridional overturning circulation has slowed by about 30 percent between 1957 and 2004.” The greenhouse crusade went wild, the media produced widespread coverage of Bryden’s findings, and the public was warned that the oceanic response to the build up of greenhouse gases could produce catastrophic results, particularly for European countries.

The story was straight out of “The Day After Tomorrow.” We were all told that the meridional circulation of the Atlantic carries warm upper waters into the mid-to-high latitudes and returns cold deep water southward across the Equator. We all learned about the “thermohaline circulation” that is a critical component in the energy balance of the earth-atmosphere system. The Bryden et al. findings could only heighten fears that human activities were having a profound impact on air-sea interactions, and if you recall, this could only lead to climate disasters – the entire story was straight out of a movie set.

We at World Climate Report were skeptical and questioned immediately why a 30 percent reduction in the thermohaline circulation had not produced noticeable cooling effects in Europe, after all, a complete shutdown of the circulation is expected to cause a cooling of 4°C in Europe, according to some computer models. We pointed out that the literature on ocean circulation contained evidence that the thermohaline circulation may be strengthening, exactly opposite what Bryden et al. claimed to have found.

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Do you recall seeing the classic film Day After Tomorrow? The theme of the movie was that humans warmed the earth, the global hydrological cycle was severely disrupted, fresh water began flowing into the North Atlantic, the Gulf Stream slowed rather suddenly, and Europe, and then the rest of the world, plunged into a glacial state. If you did not get the message in that film, Al Gore raised the possibility in his recent thriller.

But one is hard pressed to find evidence to support the idea that this is a real possibility. While there are some articles in the professional literature suggesting that the freshening of the waters of the North Atlantic has already begun, the conclusions in these articles are far from being universally accepted, and even farther from being the last word. There also exist articles showing no theoretical or empirical evidence to support the Gulf Stream story as it is pitched by Gore and followers.
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A new paper by Jeff Knight and colleagues finds further evidence to support their findings, reported last year, that the Atlantic Multidecadal Oscillation (AMO) is a real, physical phenomenon (as opposed to a statistical artifact) involving multidecadal variations in surface temperature primarily in the North Atlantic region and that its oscillations have consequences on regional climate, including North Atlantic tropical cyclones.

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