There could be a lot more than lawn chairs out of place after the next big storm.Photo: Downtown Traveler

Cross-posted from Climate Central.

New York City dodged a bullet with Irene, but big trouble passed more closely than most people think. If the storm surge had pushed New York Harbor about one inch higher, it could have been enough to overcome some of Lower Manhattan’s outer defenses and flood the subway system, FDR Drive, PATH, and the Brooklyn-Battery Tunnel, if history is a guide.

At 8:42 a.m. on Sunday morning, close to the peak of an unusually tall high tide, the water reached 4.8 feet above the average high tide level, as measured by a gauge at the Battery. It was the sixth-highest level ever recorded for New York Harbor. The tallest mark came in 1821, at 6.5 feet. The most recent incident topping Irene was the December Nor’easter of 1992, which reached about one inch higher at the Battery and caused enough area flooding to shut down the entire subway system and PATH for several days. Unless the city has substantially raised its defenses, 4.8 feet put Irene in risky territory.

Lots of things could have tipped the balance this time, but didn’t. If Irene had moved more quickly, or blown more fiercely; if it had arrived about 12 hours earlier, during a slightly higher tide. But perhaps the most important element shaping Irene’s outcome was the year it blew in.  

For more than a century, sea level has been creeping up, about 16 inches since the Civil War and still rising. If the great hurricane of 1821 had taken place today, it would have reached about eight feet above the high tide line, obliterating all records and a lot of infrastructure.

If Irene were to repeat in 2021 instead of 2011, we could very likely be writing a different story — because in 2021 the average sea level in New York Harbor will be an inch or so higher than it is today, assuming trends continue. 

So why is sea level rising? Mostly because of global warming, which is heating and expanding ocean water, and collapsing glaciers and ice sheets. In New York, the land is also slowly sinking, a few inches per century. 

Rising seas are a process well under way, not mere speculation. The New York State Sea Level Rise Task Force recently presented the legislature with metro area sea level rise projections of seven to 29 inches by mid-century, and 12 to 55 inches by the 2080s. The range of possibilities is largely due to uncertainty around how rapidly the great polar ice sheets will decay.

Sea level rise will amplify the impact of future hurricanes and Nor’easters. If we replay the 20th century, but add an extra foot of sea level at the start (the extra foot we indeed started with in 2000, compared to 1900), about six events would produce higher water levels than the Nor’easter of 1992.

But this is a very conservative estimate, because it assumes that sea level will rise this century at the same pace it did last century — when in fact we expect much more. If we crudely replay the 20th century, but add an extra two feet of water at the start — overestimating floods early on but underestimating them later — we would see about 30 critical events. 

This is how coastal places everywhere will experience sea level rise: previously rare floods will become common — soon — and the new rare floods will be outside of anyone’s experience. It won’t be a matter of just waking up one day to find the high tide at your doorstep.

New York City workers piled sandbags on and around subway grates and other vulnerable areas. If Irene had crept much higher, these measures might not have prevented major damage. 

The big lessons from Irene: Invest in more significant defenses, and get a handle on climate change. If not, we will be measuring our future woes in feet, not inches.

Cross-posted from Climate Central.

In many parts of the U.S. March went out like a lion this year.

But a new interactive map of high-resolution climate projections from Climate Central promises much tamer, warmer Marches in the future. In fact, freezing March temperatures will retreat northward this century like a routed army. (The retreat would slow to about half the speed under a low carbon pollution scenario.)

Click on the image above to view the map.

Of course, the idea of thawing temperatures seems pretty nice at the end of a long, snowy winter like the one we just had in parts of the U.S., and the trend does promise earlier starts for golfers, gardeners, and farmers in the future.

But warmer Marches also mean earlier snowmelt — and that’s got some rather different consequences. Across the American West, early snowmelt years have already been linked to drier rivers and forests later in summer and to much higher wildfire activity (see this video on the fire situation in Washington State). Scientists project these problems will worsen with further warming. And water shortages will present challenges for farm irrigation and trouble for trout and other cold-water stream life (explored more in this video about Montana).

Climate Central‘s maps show what will happen to average March temperatures if we continue to emit carbon at today’s high rate. By the end of this century, all states analyzed will experience a majority or near complete loss of areas in which average March temperatures are currently below freezing. The biggest losers, in terms of total area, will be Minnesota, Montana, and North Dakota; but seven states, from Arizona to Wisconsin, are projected to lose just about all their frozen March acreage. (For a full tally, see this table.)

It’s interesting to note that while Washington, D.C. had record-breaking winter snows this year, March temperatures in the nation’s capitol never dipped below freezing — a new record for warmth.

Speaking of warmth, the thaw season has just begun in the Arctic. Over recent decades, the Arctic has been the fastest-warming region on the planet, a pattern scientists expect to continue. Arctic warming trends and their consequences — shown in this new video short (based mainly on NASA satellite data) — make projections of March warming in the U.S. look tame.

Click on the image above to watch the video.

For example, Greenland is shedding ice at a rapid pace; the average net loss per year from 2004 to 2007 was about 25 times greater than the average from 1992-2002. How much of this shift may have come from natural variation and how much from human-caused warming is difficult to assess. But two things are clear: Arctic warming means Greenland ice loss, and Greenland ice loss means rising seas. Recent scientific studies that take Arctic trends into account generally project more than a three-foot rise in sea level this century.

Another key trend just coming to light is that the crust of ice that covers parts of the Arctic Ocean has been getting thinner. Most observers have focused on the shrinking extent of Arctic sea ice. But the ice appears to be thinning even faster. Just-published research (subscription required) suggests that the ice may be thinner than we thought, a troubling finding since thinner ice is more vulnerable to future disintegration.

Bright, white sea ice reflects the sun’s energy back into space — like a giant planetary heat shield. As sea ice disappears, more dark ocean is exposed, absorbing more of the sun’s heat, and accelerating Arctic warming.

So, as we dump our winter coats and turn our minds to spring — let’s take a moment to celebrate the cold days of March, while they’re still with us!

Magicians divert us with wands and puffs of smoke. Bullfighters fool steers with flashes of cape at just the right moment. Even Shakespeare understood: Things in motion sooner catch the eye than what not stirs.

The human brain likes movement, and that makes it poorly equipped to think about climate change. Scientists warn that, on our current course, the planet could warm as much as 10 degrees F this century with catastrophic consequences. But since the temperature fluctuates more than 10 degrees every day in most places, it’s easy to see why many people might not be worried.

Critics have recently proclaimed we are in a period of global cooling, because most years since have not rivaled the record heat of 1998. But thats like saying summer is not coming because of some cool days in May. The claim of recent global cooling has no statistical basis, and distracts us from seeing an almost century-long warming trend.

The current controversy over email stolen from climate scientists looks like another trick of distraction, with a well-timed release just a few weeks before an international climate summit in Copenhagen, but at least a month after the email appears to have been originally hacked.

Certain uncovered notes definitely catch the eye. Passages show contempt for climate change critics, plans to exclude contrarian research from a major international report, and ideas for cosmetic treatment of data displays. While some authors seem to have felt frustrated and persecuted by the political atmosphere, this cannot excuse any inappropriate actions any might have taken — an open question currently without definitive answer (an investigation is underway).

Our understanding of climate change is like a great ocean liner steaming forward, and these emails are but a wisp of smoke from the pipe. The greatest expression of this understanding, to date, is the three-volume Fourth Assessment Report of the Intergovernmental Panel on Climate Change, published in 2007. Almost one thousand scientists from over one hundred countries wrote the report, drawing upon many thousands of research papers (including the ones the email correspondents did not like — in the same chapter that they coordinated), and tens of thousands of data series, redundantly confirming the same trends again and again and again.

That is what gives scientists the most confidence: when numerous and independent lines of research reach the same conclusions. Even Roger A. Pielke Sr., a frequent critic of mainstream climate science, has written that it would be irrelevant if the email correspondents did fudge their temperature data improperly — a case far from settled. Why? Other groups using other methods found the same warming trends. And if you dont trust thermometers at all, its hard to argue with melting ice masses and rising seas around the world.

In short: do not be conned by the flash and speed of an email scandal. The real action is with the glaciers.

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