The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change


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When the Sky Does Not Make Sense

As I explained on Tuesday, the East Coast of the US has been pummeled recently by horrible weather. The worse of the flooding struck South Carolina, but the storm caused flooding every state from Georgia north to Maine and inland as far as Ohio. The storm was remarkable for many reasons, not least because of its vast size and the shear amount of water that fell out of it:

  • In Maine, Caribou, Millinocket, Houlton, and Portland all broke daily rainfall records–Portland’s new record is double the previous record, which was set in 1922. One area, Searsport, received more than ten inches in total from the storm.
  • In Massachusetts, Boston almost doubled its daily rainfall record, previously set in 1899. The worst of the rain had not get moved through the state at that point.
  • In Rhode Island, Provincetown set a new daily record and New Bedford had to shut down Route 18 for two hours due to flooding.
  • Some parts of South Carolina got one or two feet of water out of the storm in total. Dams breached, highways flooded, and caskets literally floated up and out of their graves.

Coastal flooding–a storm surge driven by wind–was just as bad and, in some areas, worse. Just as unprecedented as the flooding was the storm’s structure–record-breaking floods in this part of the world are categorically hurricanes or tropical storms, but this was neither. There is simply nothing in the record-books remotely comparable.

There was a hurricane involved, though.

Hurricane Joaquin was an extremely strong Category 4 storm–its strongest sustained winds were just 2 mph shy of qualifying as a Cat 5. Hurricanes of this intensity are extremely rare–the last one in the Atlantic was five years ago. It hammered the Bahamas and sank a cargo ship with all hands. It never made landfall in the US, but its influence sent high surf along the length of the Eastern Seaboard (in Maine I heard surf about a mile inland–and the closest water is a protected cove that typically has no waves) and contributed to the huge storm surge in the South. The hurricane and the un-named storm were close enough to influence each other, with the monster un-named stormed steering Joaquin and the hurricane funneling moisture into its extratropical partner. This relationship between two storms was also highly unusual and was one of the reasons that meteorologists had trouble developing forecasts for Joaquin.

Detractors sometimes complain that any time the weather gets weird, somebody cries “climate change.” The reason for that is that an altered climate means weird weather. A climate is essentially the normal pattern of weather in a given area–or across the entire planet. When the pattern of typical weather changes, that is, by definition, climate change.

But what are the links between this particular weather event and the greenhouse effect?

Most directly, the sea is higher. Any time you get a storm surge, that surge is worse than it would have been because the sea starts out higher. The difference is only about eight inches (some areas see much greater effective rise because the land is also subsiding), but that is enough to have a huge effect. Anyone who doubts that should imagine the difference between zero and eight inches of water in their living room. Or, for that matter, the difference between zero inches and one inch! Last week’s storm pushed seawater up onto the land in South Carolina, North Carolina, Virginia, Maryland, Delaware, New Jersey, and Massachusetts. Today I saw, posted on Facebook, a video of a shark cruising down a flooded street in West Ocean City less than ten miles from my house. People who live in the affected areas can now go out and see exactly what climate change looks like simply by holding a ruler up to the high water marks. That’s about as unambiguous as it gets.

Secondarily, the sea over which Joaquin intensified was unusually warm–at least as of August, that area actually had record-breaking warmth. Warm water feeds hurricanes, so this pool of warm water explains Joaquin’s unusual strength. And Joaquin helps explain the huge amount of moisture in the un-named storm. Pools of warm water, like pools of warm air (heat waves) come and go, but global warming means they are more intense and more frequent now.

Third, a warmer planet means more extreme weather, including more extreme rain events. Again, the issue is frequency. This past week’s event was a thousand-year storm–that’s not a schedule but an expression of probability. The chance of such a storm occurring in any given year is about one in a thousand or 0.1%. Yes, it was certainly possible to get more than one per millennium, just as it’s possible to flip a coin and get heads seventeen times in a row, but you wouldn’t expect it. With extreme rain events happening more often, now we can expect these more often. I doubt this past week’s records will be broken any time soon, these things are still going to be pretty rare, but what isn’t going to be rare is the breaking of some record somewhere, especially those that involve precipitation (including snow!) or drought, or heat.

“We’ve never seen anything like this before!” is what climate change sounds like.


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What Scientists Don’t Know

So, sea level rise has been in the news, recently, in part  because of recent warnings from Dr. James Hansen that we could see as much as ten feet of rise in the coming decades. The story is a little more complicated than that and has caused significant controversy. In the interests of clarity, I’ll summarize what I’ve been able to learn about Dr. Hansen’s announcement and also explore the overall topic of sea level rise.

According to Ars Technica, Dr. Hansen and his colleagues have completed a research project that involved using a computer model to explore how ocean currents would respond to various speeds of sea level rise. They could set the model to “ten feet in fifty years,” and the computer would show them ocean currents for that scenario. The study did not look at how much the sea will actually rise how quickly, only at the consequences of different rise scenarios. Then, the team submitted a paper on their research to a peer-reviewed journal, but the review process can take a long time. The team evidently wanted their results to support meaningful climate action at the Paris conference in December, and worried that the paper might not be published in time. So, they chose a journal that has an unusual public peer-review process, enabling the researchers to speak publicly about their results before the review is complete. As part of getting the word out, they also released a short summary of their research, which included speculation that the sea could in fact rise ten feet in the next several decades–something this particular research project did not address, but Dr. Hansen is entitled to make educated guesses in his area of expertise.

The problem is that the wording of the summary leaves it unclear that he is speculating, and the public media have generally reported that the study actually predicted a rapid ten-foot rise–something that is well beyond scientific consensus at this point. To be clear, that doesn’t mean the rapid rise won’t happen. It probably could, because Dr. Hansen is very much an expert on the subject, and he could turn out to be right. He is not in any way misrepresenting his research, he is just talking about something else besides his research and doing it in a way that leaves the distinction between the two unclear.

Here is an analogy:

Say that an auto-safety researcher conducts a series of crash-tests and concludes that a given model of car has a design flaw such that a particular type of crash is lethal at an unusually low speed. She then calls a press conference, presents her findings, and says “given my results, I am especially concerned about young drivers–the traffic mortality of drivers in the 16-to-21 age group may sky-rocket if the manufacturer does not correct the flaw.” The media then respond by saying that safety test predicts teen driver mortality to sky-rocket, even though that isn’t at all what the test was about.

It is possible that Dr. Hansen created the current media buzz deliberately in order to get attention for his cause–but if he’s being alarmist, it’s only because we are in an emergency that deserves the sounding of alarms. It’s not wrong to shout “FIRE!” if the crowded theater is, in fact on fire.

I expect climate denialists will pounce on this one and paint it as an episode of deliberate dishonesty, but they would probably find a way to do that no matter what Dr. Hansen decided to say.

So, here is the overall situation with sea-level rise as we know it so far:

The world is warming, and has been for some time, now. That’s not a prediction, it’s simply historical fact. It can be difficult to measure the rise in any one location because not only does the sea go up and down, but so does the land. In much of New England, for example, the land is very gradually rising because it is still rebounding from the weight of the glaciers of the last ice-age. That makes it harder to notice sea-level rise on New England coasts. In contrast, my home area, in Maryland, is sinking, making sea-level rise seem faster than it really is. But by comparing multiple sites, measuring from satellites, and other techniques, scientists can work out how fast the seas are actually getting bigger; the water has risen about eight inches since the Industrial Revolution. Most of that rise is due to thermal expansion–warm water takes up more space than cold water. The rest is due to meltwater from glaciers.

Glaciers anywhere in the world, even those that are nowhere near the sea, raise the sea level as they melt because the meltwater eventually flows into the sea. We know how much ice is currently locked up in glaciers, so we know how much the sea could rise if all of it melted. And because all that ice takes a long time to melt, we know that even if the global temperature stabilized tomorrow, the ice would continue to melt and the sea would continue to rise until the world caught up to its new temperature. What we don’t know is how fast the ice will melt or exactly how much melting we have already committed itself to.

Not all ice has an effect on sea level, however. Floating ice–either sea ice, which forms when the ocean surface freezes, or icebergs, which form when chunks of glacier break off and land in the sea, can melt without changing the sea level at all. To demonstrate this, fill a glass with tap-water, drop a few ice cubes in, and carefully mark the water level. Allow the ice cubes to melt, and you’ll see that the water level remains unchanged. This is because when ice melts it shrinks and the volume it displaces when it floats is precisely equal to the volume of water it turns into. The melting of the arctic sea ice is a terrible catastrophe, but it’s irrelevant to sea level rise. The fact that sea ice around Antarctica is growing (remember that warmed-up ice remains ice until it reaches 32 degrees, and Antarctica is very cold) is also irrelevant.

What does matter is how much ice is floating in the sea, so if a glacier starts calving off icebergs faster (as many glaciers are), that raises the sea-level, even if those floating icebergs don’t melt. Also, much of the ice surrounding Antarctica is actually sitting on the sea-bed. That is, the glaciers rest on solid rock, and that rock is below sea level. If those glaciers thin to the point that they begin to float, then not only does the water that melted off them raise the sea, so does the fact that they are floating. One of the scary things about the science here is that it’s not always obvious from the surface which ice has begun to float–there are tests scientists can do, but those tests sometimes give surprisingly bad news.

We’ve had a lot of bad news from glaciers recently, some of which have moved very quickly, broken apart, or melted away quite unexpectedly because of reactions below the surface that scientists did not anticipate. We’ve never seen the world warm this quickly before, so we don’t know what ice does in situations like this. That is one reason why Dr. Hansen could be right–although the speeded-up melting he warns about has not happened yet, and nothing we know about ice suggests it is going to happen, there is a lot we still don’t know about ice.

Dr. Hansen is guessing that what we don’t know will hurt us.


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Bigger Floods in Texas, Reprise

Texas is flooding again, unfortunately.

Tropical Storm Bill formed in the Gulf of Mexico overnight and is–right now, as I write this–coming ashore between Houston and Corpus Christi. Bill is “only” a tropical storm, not a hurricane, but that ranking depends on wind speed, not on overall severity. Tropical storms, by definition, have sustained wind speeds somewhere between 40 and 74 miles per hour–any more, and they become hurricanes, which Bill will not do because these storms can generally only strengthen over water. Bill is not a very windy storm; its highest gusts are likely to be around 50 MPH. But the real problem is flooding.

Historically, most of the people who die in hurricanes and tropical storms drown.

The flooding is from two sources, rain and storm-surge, although the two interact in coastal areas if the storm surge makes it harder for rainwater to drain away. How much rain falls is not just a factor of how much moisture is in the clouds (typically a lot, but it can very) but also how big the storm is and how fast it moves. A large, slow storm takes longer to move over any given area and therefor rains more. Bill is about as wide as the Gulf Coast of Texas–big, but not monstrous. I have not learned whether it is slow-moving.  An old frontal boundary across Arkansas and North Texas will likely merge with Bill, adding more moisture to the system. A sickle-shaped area across parts of Texas, Oklahoma, Arkansas, Kansas, and Illinois is now under a flash flood watch. A much larger sickle of less severe rain reaches all the way to Maryland (which is ok, we need it).

Storm surges are caused by winds and pressure changes pushing along a dome of sea water. The surge looks something like a very rapid, unusually high tide–it can roll in within a few minutes. Before the modern era of accurate storm tracking, people sometimes went down to the beach to watch dramatic surf and then died as unexpected storm surges came in faster than they could run. Tropical Storm Bill’s winds are fairly modest, so its surge is only about four feet at the most, but the storm is rolling in at high tide–and we’re close to the New Moon right now, so this is one of the highest tides of the month. So, while we’re not looking at a monster surge by any means, Bill’s timing makes it worse than it might otherwise have been.

Again, this is weather, not climate. While human-caused climate change underlies all weather, just as a rising tide underlies all waves, this tropical storm is not, all by itself, a climate change story. So far, Bill looks like the same kind of storm the Southern US has always been vulnerable to. But what is a climate-change story is the context into which this storm is now moving.

First and foremost, Texas and Oklahoma are already soaked from weeks of intense, sometimes disastrous rain (following years of horrible drought). When the ground is already wet and rivers are already high, it doesn’t take much more rain to cause a major flood all over again. And while some flooding has always been a fact of life, the rapid swing from drought to weeks of torrential rain has all the hallmarks of the new, globally-warmed normal of extreme weather. It is because of this recent history of saturated ground that I am frankly worried about my friends and family in Texas right now.

Of course, Bill’s storm surge is also eight inches higher than it would have been were it not for sea-level rise–both from seawater expanding as it warms up and from the melting of glaciers. Eight inches might not seem like a lot, but imagine the difference between zero and eight inches of salt water inside your house.

Finally, according to a Alan Weisman, whose really neat book, The World Without Us, I have just read, the Gulf Coast of Texas is now uniquely vulnerable to storm surges because of the oil industry:

When oil, gas, or groundwater is pumped from beneath the surface, land settles into the space it occupied. Subsidence has lowered parts of Galveston 10 feet. An upscale subdivision in Baytown, north of Texas City, dropped so low that it drowned during Hurricane Alicia in 1983 and is now a wetlands nature preserve. Little of the Gulf Coast is more than three feet above sea level, and parts of Houston actually dip below it. –p. 143

So, a storm surge coming ashore near Galveston of “only” two to four feet is really serious business. Petrochemical extraction is not itself climate change, but it’s obviously intimately related.

This is not the first Tropical Storm Bill, nor will it be the last. Meteorologists reuse storm names, only retiring those that, like Katrina, become particularly note-worthy. None of the previous Bills has earned that distinction, and this one probably won’t, either. But we live in a world where even modest storms are more destructive than they might otherwise have been.


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Hot News from Down South

The latest climate news to light up social media is that Antarctica has hit a new, all-time record high of 63° F.

According to CNBC,

A single temperature event doesn’t make a trend, but it’s a situation worth watching, said Jordan Gerth, a researcher at the Cooperative Institute for Meteorological Satellite Studies. “One rare temperature doesn’t tell us a whole lot,” Gerth said. “But if we see these events happening more frequently over the next decade or so, it could be a larger story to tell.”

This comment is a strange one. I’m going to give Dr. Gerth the benefit of the doubt and assume he is being misrepresented or misunderstood, somehow, but the implications of the quote are worth discussing.

It is quite true that one event does not make a trend. Without context, an extreme weather event is not evidence of anything because even if our climate were not changing, the occasional hot day would still occur. To find the footprint of climate change, you need to look at weather records over time. But then, why can’t we just look at Antarctica’s weather records over time and determine if there is a trend? Dr. Gerth appears to think we can’t do that for some reason, but must look to the future instead. Either that, or his words might be taken to mean global warming has not been conclusively spotted in Antarctica yet.

And that is rather patently not true.

I am inclined to think Dr. Gerth meant that there isn’t enough data on Antarctic weather to draw conclusions. Frankly, I don’t see how there could be much weather data on the frozen continent, given how sparsely populated it is and how recent the human presence is there. There are, indeed, weather stations on Antarctica, some of them the better part of a century old, though their records are not necessarily continuous–but there aren’t very many of them. Until the age of weather satellites, there must have been huge swaths of the continent where any weather could have been happening at all and no one would know. The signal of climate only emerges from the noise of weather once you have about thirty years of data to look at and the satellite temperature record is only 37 years old.

Antarctica is also fairly big and some of its associated islands (including the sites of the recent temperature records) are actually well outside the Antarctic Circle. The emotional punch of the headline (“Antarctica tops 60°!”) is a bit misleading, given the tendency of the outside world to equate all of Antarctica with the South Pole.

And yet we do have a fairly simple way to tell that Antarctica’s temperatures are indeed going up; the sea level is rising. About half of the observed rise is due to melting ice, as opposed to thermal expansion and other factors, and much of that ice was in Antarctica. Even if we had no weather data for that continent at all, we would know its climate is warming.

We also do have long-term climate data for the south of the world,quite apart from weather stations. The glacial ice records evidence of temperature, along with other important information, such as atmospheric composition, in layers, for thousands of years. A British team drilled in and got a sample some years back:

What the scientists discovered, however, removed any doubt. “We found that the peninsula has been warming for the past 600 years,” said lead author Robert Mulvaney, of the British Antarctic Survey, in an interview. “But the rate of warming has been much faster during the past century, and fastest over the past 50 years.”

From this and other studies, we know that Antarctica is warming, and is in fact warming faster than anywhere else in the world. Also, Antarctica is not the only place that has set a new heat record recently: Equatorial Guinea, Ghana, Samoa, and the Wallis and Futuna Territory have all either set or tied their high temperature records in 2015. Five national or territorial heat records in a year not quite four months old yet is remarkable, especially as exactly zero have set cold records (sorry, Boston).

So why did CNBC quote Dr. Gerth as saying there is no larger story to tell?

There is, in fact, a regional story here as well as a global one, and it’s an oddly familiar story for those of us in the United States since it involves the polar vortex.

Polar vortexes are not some unusual type of winter storm, popular media representations to the contrary. Instead, they are simply the cold air masses around the poles. The boundaries between these air masses and more temperate air are quite abrupt and marked by currents of upper-air winds–the jet streams. The location of the boundary changes, sometimes developing huge meanders that bring unusual temperatures to unusual places. Over the past few years, we in the United States have seen several such events in which the Southeast of our country froze while Alaska (and many other places) saw record warmth.

The recent unusual warmth in parts of Antarctica is also due to a wavy polar boundary and was also associated with unusually cold temperatures (even for Antarctica) elsewhere on the continent. The same wind pattern was also responsible for the other major climate-related news story, the flooding of the Atacama Desert, in Chile. While the rainstorms only brought about an inch of water, that is as much as the area usually gets in fourteen years. And with little vegetation to absorb water or stabilize the ground, the floods were dramatic.

Now, I’ve written before about the link between melting Arctic sea ice and the recently wavy polar boundary, but I do not know if an equivalent process is at work in the south. It may well not be, since Antarctic sea ice is actually expanding. The sea and air are both steadily warming, but both are still cold enough to allow ice to form in the Southern Sea–meanwhile, wind and water currents that previously limited sea ice are changing, allowing more ice to form (sea ice has no effect on lea level; the land-based ice that does influence sea level is melting rapidly).

So, is this particular extreme weather event related to global warming in an clear, causal way? I do not know. But when an entire system changes, it is unrealistic to expect any corner of that system to remain untouched.


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Conversation with a Skeptic

This is a rewritten version of a piece I wrote in college–it is a fictional representation of mt attempt to play “devil’s advocate” with what I knew about climate change at the time. The character of Skeptico is entirely fictional. The information in the piece came largely from the book, Global Warming: The Complete Briefing, by John Houghton, from Cambridge University Press. It’s an excellent book, but it was written in 1997, so if you read it, remember the case for climate change being real has grown even stronger in the past seventeen years.

I remember posting this piece here, but cannot find it in the archive, so I’m posting it again.

Let us say that I sit down on the edge of the dock next to my friend, the climate skeptic, whom we will call Skeptico. The tide is up, so I can swish my bare feet in the water, as my companion is already doing. We admire the view in silence together for a few minutes before either of us speaks.

“I don’t get why you environmentalists have to be so negative,” he says. “Look at this! It’s beautiful. If you had your way, no one would ever see this, no one would fish here, no one would get to enjoy this…all these things take fossil fuels. I don’t think we should consider getting rid of all the modern conveniences that let so many people enjoy the environment in the first place.”

“Is that a rhetorical statement or a real question?” I ask. “Do you want to talk about why I do the things I do?”

“Yeah, I do, actually.”

“Ok,” I begin, “you mentioned fossil fuels. It sounds as though you don’t think their use should be limited. That implies that you don’t think global warming is a problem. Is that true?”

“Yes, that’s true. I don’t think we should give up things we want and need and worked hard to get just because of some unproven theory.”

“Why do you call it an unproven theory?”

“Well, that’s what it is, right? It’s just a theory, it’s not fact.” Skeptico seems almost angry, saying this, and fidgets a bit. I think for a minute.

“Sounds like you’re saying that theories are ideas that are not yet proven, that when it is proven, it graduates to fact-hood.”

“Right.”

“Ok, that’s not what a theory is, not the way scientists use the term, anyway. Theories are attempts to organize and explain the things you know so you can make educated guesses about the things you don’t know. Like if I know why the water is warm today I can get a good idea whether the water will be warm tomorrow. Makes sense so far?”

“Yeah, I know what a theory is,” replied Skeptico, irritably, “but theories do change. They say one thing this year, another thing the next. You can’t tell me that a theory is the same thing as a fact.”

“No, I’m saying a theory is a completely different thing than a fact. You’re right, theories do change, and sometimes they are abandoned altogether and replaced. But that doesn’t mean that theories are just guesses; theories are the ideas with which we make guesses. The more consistently right the guesses are, the more reliable the theory is. When high tide was yesterday is a fact. We can use a theory about tides to predict when high tide will be today—and that’s reliable enough that you’ll plan your day around it so you can go fishing. I’ve seen you do it.”

“You know it like a poet,” Skeptico replies, but seems slightly embarrassed and lapses into thought for a moment before speaking again. “Oh, so when they say ‘theoretically, such and such is true,’ they’re guessing, but the guess isn’t a theory–it’s theoretical because a theory generated it?” My friend seems pleased by this insight, but frowns again a moment later. “But why is global warming a reliable theory? I don’t see the sea level rising.”

“You don’t? This island was wider ten years ago,” I point out.

“That’s erosion from storms. That’s different.”

“I’m not so sure about that,” I respond, “but in any case, global warming isn’t a theory, it’s data. The greenhouse effect is a theory.”

“That’s just rhetorical,” Skeptico protests. “It’s not my fault if I don’t use exactly the right terms. You know what I mean!”

“No, it isn’t rhetorical. Global warming isn’t a theory because ‘global warming’ just means the globe is getting warmer—which it is. It’s been measured. That’s data, not an explanation of data. The theories are about why the globe is warming and what is going to happen next.”

“Ok, well, either way, how do we know the theory is reliable?”

“Because it’s the same set of theories they use to predict the weather.”

“The weather! Weather predictions are completely unreliable!” Skeptico scoffs.

“Really?” I challenge. “It’s not exact, but in the last few years they’ve gotten pretty good. I’ve seen you decide not to go out on the water when they’re predicting thunderstorms. Weekly outlooks are usually right, and they can predict the track of hurricanes within a few hundred miles a week ahead of time.”

“Ok, that’s a few days. That’s different than the decades you’re talking about with climate change.”

“There are longer-term predictions as well, like for El Niño-related events. It all depends on what kind of simulation the computers run. But there is a lot of overlap in both theory and data for climate vs. weather. And the weather reports are accurate enough to act on, so the climate predictions should be, too.”

“Ok, that makes some sense. But I’m still not going to just take some weatherman’s word for it.”

“Nor should you,” I say. “Listen, at their most basic, these theories are pretty simple. The idea is that several of the gases modern human activity produces trap heat. As the atmospheric concentration of these gases rise, so does the global temperature, creating all sorts of problems. That’s the idea on the table here. Where do you see weaknesses?”

“How do we know the planet as a whole is getting warmer? Couldn’t it just be some kind of sampling error? Or some kind of natural cycle?”

“They compile measurements from all over the planet and take an average. They can also chemically analyze the air bubbles in glaciers to see what temperature the air was when the snow originally fell—that’s not enough to get a global average from, but it does go back many thousands of years, and ice cores can be taken at many locations all over the planet and compared. According to that record, the warming over the recent few decades is not normal.”

“How do we know these gasses trap heat? Has that been proven?”

“Basically, yes, it has. For example, was identified as a greenhouse gas back in the eighteen hundreds. I can look up the names of the people who made the discovery if you like, when we get back to the computer lab. The Earth doesn’t actually receive enough sunlight to account for the planet being as warm as it is, unless something in the atmosphere were trapping heat. When CO2 was first identified as a greenhouse gas, they calculated out what would happen if carbon dioxide concentrations increased, and they came very close to predicting the actual warming we’ve experienced. Wouldn’t it be strange if their theories were wrong but something else heated up the planet exactly as if they were right?”

“Ok, but what if carbon dioxide levels aren’t rising? Is that possible?”

“If carbon dioxide levels aren’t rising, where else is all the carbon dioxide released by modern industry going?”

“Oh.”

“Yeah. Anyway, changing carbon dioxide levels have been measured, too. I suppose—theoretically—that data could be wrong, but there’s so much data involved from so many different sources that would have to be an awfully big foul-up or a ridiculously vast conspiracy. If we’re going to go there, we might as well say nothing is reliable ever, which is not particularly realistic.”

“Ok, but we’ve been talking about a simple version of these theories, right? It’s not really simple. I’ve read articles about these things, how increased cloud cover could block a lot of sunlight, or how melting ice in the North Atlantic could change ocean currents and cause another ice age…even if in the simple version the Earth would continue to warm, how do we know what will happen in real life where things aren’t simple?”

“Well, most of that detail, is accounted for in those computer programs. That’s why climate predictions require so much computer power to calculate. Yes, it’s possible some undiscovered something will fix the problem or buy us more time, but it’s equally possible that some surprise will make things much worse. There have been a couple of nasty surprises already, like Antarctic and Greenland ice melting much faster than expected.”

“I heard about that, but I don’t really know who to believe. You don’t even think scientists are always right–you take vitamins with no established daily value, you’d rather take unproven herbal things than medicine….”

Ooh, touché! I chuckle a bit before speaking.

“I question mainstream science; I don’t reject it wholesale. I question everything, as do you, which is why we get along. Look, if modern science was completely out to lunch, modern technology wouldn’t work as well as it does, and it clearly does work. One aspect of science is an extended community of people who share data and check each others’ conclusions. Sure, sometimes they still make mistakes, but the system works well enough that we’ve created the modern world. So, when the top scientists of almost every country in the world say an issue is important, I pay attention.”

The tide has ebbed while we talked; I can’t reach the water with my feet now. The swallows that darted over the water after insects by day have been replaced by bats as night comes on. We watch the bay turn pink and silvery under the reflected light of the fading sunset and then Skeptico speaks again.

“Ok, so we know the temperature is rising because it’s been measured. We know the atmospheric concentration of greenhouse gases is rising because that’s been measured, and anyway, where else are the gases we produce going besides the sky? We know they are greenhouse gases because they have been studied by chemists whose predictions proved reliable, and we know rising temperatures are going to cause problems because weather forecasters say so and they’re usually at least partly right. We know all this isn’t the product of some wild-haired maverick because many well-respected scientists agree with it, and we can’t just assume that all of them are crazy together because if they weren’t right most of the time modern technology wouldn’t work. That’s an answer for everything…but I still don’t know. I don’t know if I trust mainstream science.”

“Look, I’m not saying to trust them. I’m saying think about what is most likely. Do you really want to bet the future of life on Earth that thousands of the most intelligent and well-educated people on the planet are all wrong at the same time in the same way?  And that their “mistake” actually conforms to common sense in most respects? I mean, you read the news. Does it look like the weather has been normal for the past decade or so?”

“Do you want to bet the economy that they’re right?”

“Who said the economy is really on the line here? Isn’t using less petroleum and wasting less energy a good idea anyway?”

“That’s another conversation.”

“Yes, probably for another time. I’m getting bit up. But think about it. When you do arithmetic, how do you check your answers? You do the problem again, right? Maybe you even do it two different ways. If you get the same answer, that means you’re right, right? If your only remaining argument against anthropogenic climate change is to suggest that thousands of scientists all made the same mistake over and over again for decades on end, that really doesn’t sound too convincing.”

“No, I suppose not. I still want to think about this, though.

“Good. Thinking things through is good,” I say.

Skeptico gets up, stretches a bit, and fumbles for shoes. Neither of us thought to bring a flashlight, although the moon is almost full and should make additional light unnecessary. I fish a bottle of bug spray out of my pack, explaining that I plan to stay out a bit longer. Before going, Skeptico turns to me and thanks me for our conversation.

“I didn’t think you’d actually talk to me about this stuff, but you really took my questions seriously.”

“And neither of us died!” I laugh. “Good night!”

“Good night. See you tomorrow.” And my friend walks off.