What Are The Measured Impacts Of Anthropogenic Climate Change To Date?

I really want to know the answer or answers to that question. I’d really like to see a list that scientists from both sides can agree on.

My impression from reading about global warming every day since 2008 is that there are few if any measurable impacts so far–with two notable exceptions.

Human contributions to global warming are generally thought to have commenced on an industrial scale during or shortly after World War II. However, temperatures chose just that time frame to have a 30-year lull that resembles nothing so much as the recent ‘stall’ in temperatures since 1998, noted by skeptics everywhere and James Hansen, if nobody else on the activist side.

Temperatures then rose rapidly between 1975 or so and 1998 or so, amounting to about 0.5C. What has that done to our planet?

The one thing most everyone agrees on is that the Arctic has been affected–temperature rises there were not 0.5C but closer to 2C. There isn’t as much ice as before 1975 and it melts more extensively in the summer. The IPCC also estimates that the duration of ice cover over rivers and lakes has decreased by two weeks over the course of the 20th Century in the mid and high latitudes of the Northern Hemisphere. They also note a lengthening of the growing season by four days on average.

But what else? There are hundreds–no, thousands of articles and papers on the subject but most are describing a possible future, not the present.

An ornithologist named Keith Butler of Oxford’s Department of Zoology catalogued some of the observed impacts in a paper published in 2003.

Butler writes, “Over the past century, the Earth has warmed by approximately 0.5 °C (von Storch & Navarra 1995, IPCC 1998). During the past 10 years, a variety of studies have shown that global climate change is affecting the world’s flora and fauna. The active growing season of plants has advanced by 8 days in northern latitudes (Myneni et al. 1997).”

There are other changes in species behavior. Butler continues, “Studies on birds have shown that diverse avian taxa are now nesting significantly earlier in both the United States and Europe (Kruk et al. 1996, Crick et al. 1997, Forchhammer et al. 1998, McCleery & Perrins 1998, Visser et al. 1998, Brown et al. 1999, Crick & Sparks 1999, Dunn & Winkler 1999). Surprisingly, however, a widespread change towards an earlier arrival date in migrant birds, although demonstrated on the European continent (e.g. Sokolov et al. 1998, Sparks et al. 1999, Sparks & Mason 2001, Tryjanowski et al. 2002), has not been demonstrated on the North American continent. Although a few studies have shown that individual species are altering the timing of their migration (Bildstein 1998, Inouye et al. 2000, Pulido et al. 2001), studies examining the arrival or departure dates of multiple species have shown that whereas some species are arriving significantly earlier, others are arriving significantly later (Mason 1995, Oglesby & Smith 1995, Bradley et al. 1999, Wilson et al. 2000, Zalakevicius & Zalakeviciute 2001).”

In the Discussion section of his paper Butler says that 28 of 103 species migrated earlier, and no species migrated later. But he didn’t write on whether this was good or bad for the species or those species with which they interacted.

The IPCC technical paper linked to above states categorically that ranges for plants and animals have shifted polewards and upwards. That plants flower and insects emerge earlier.

But has global warming had a positive or negative effect to date? Do we have an idea of how climate change has affected biodiversity?

The IPCC’s Technical Document describes studies of hundreds of species. They note a variety of changes. Again, most are simply that–changes. The IPCC doesn’t say whether the changes harm, have no effect or even help the species affected.

But in some cases they describe real problems. It probably comes as no surprise that some species of plants and animals are experiencing severe difficulties.

Reading the IPCC’s document it struck me that in almost every case of a species in trouble, they made it clear that climate change was a contributing factor, not the only one. And in no case did they specify climate change as the principal problem. Throughout you see sentences like,

• “…shorter term variations in North Sea cod have been related to a combination of overfishing and warming over the past 10 years.”
• …”(Coral) bleaching effects are also associated with pollution and disease…”
• …”Along the Aleutian Islands, the fish population driven by climatic events and overfishing has changed, thus changing the behavior and population size of killer whales and sea otters…”

As I’ve noted before, climate change may be expected to serve as the unwelcome straw that broke the camel’s back for some unlucky species–but the principal threats mankind poses to biodiversity are and will remain for some time to come, habitat loss, hunting, introduction of alien species and pollution. (The four horseman best described by Matt Ridley, who’s still busy disagreeing with me over on another thread. Sigh.)

Of course the iconic example of the threat to biodiversity is the polar bear. However, anyone who has been following their trials and travails will have read that their population is increasing, not decreasing, mostly due to the halt on hunting put in some decades back.

So I would submit that global warming so far has not been more than an annoyance for the biome of this planet, especially in comparison with the rest of man’s follies.

What about sea level rise? It has been rising at between 1 and 3 millimeters per year for quite some time now. Has it had an effect so far?

From Wikipedia

Sea level appears to have risen about 8 inches since 1880. Have people moved? Have storm surges been more damaging? We saw with Sandy that timing is important–the storm hit at high tide and that didn’t help. But was it made even worse by the sea level rise due to global warming?

Scott Mandia certainly thinks so. He told Chris Mooney in an article for Mother Jones “I keep telling people the one lock you have here is sea level rise,” meteorologist Scott Mandia explained to me recently. “It’s the one thing that absolutely made the storm worse that you can’t wiggle out of.” That’s… an interesting choice of words. He must have expected a challenge. He won’t get one here.

…”First, according to sea level expert Ben Strauss of Climate Central, the sea level in the New York harbor today is 15 inches higher than it was in 1880. Now, to be sure, not all of that is due global warming—land has also been subsiding. Strauss estimates that climate change—which causes sea level rise both through the melting of land-based ice, and through thermal expansion of warm ocean water—is responsible for just over half, or eight inches, of the total.”

…”But as it turns out, eight inches matters a lot. First of all, using Climate Central’s Surging Seas tool, Mandia estimated that 6,000 more people were impacted for each additional inch of sea level rise. That means, basically, that they got wet when they wouldn’t have otherwise: one inch wetter for some, eight inches wetter for others, and everything in between.”

So an extra 50,000 people may have been affected by Sandy because of global warming. And that sounds about right to me. It would be impossible to guess how badly they were affected out of the millions of victims of the storm. But 50,000 is enough to make a difference.

I need to tie this up for the evening–may return to it later. I wanted in this piece to put a line in the sand saying this is what global warming has done to date. Looking at some of the high profile impacts that have been signaled as future problems, I think we can say the following:

• The Arctic has been heavily impacted by global warming. Temperatures have risen about 2C, ice is thinner and less extensive and melts more dramatically each summer.
• We have noted real changes due to warming in the timing of seasons and the response of plants and animals to it. We haven’t see much in the way of evidence that either plants or animals have been harmed so far.
• Global warming so far amounts to an additional stressor to species already endangered by our other actions–hunting, introducing alien species, habitat loss and pollution, the sum total of which far outweighs the negative effects of climate change to date.
• Sea level rise seems to have contributed to the destructive power of storms, increasing the areas affected. This is a real effect and should not be discounted or ignored.

I’d welcome additional comments on this. I spent two hours on this post and I know it is not enough for a subject of this magnitude. But it’s what I have to offer on a Monday evening.