Reporter's notebook: A Costa Rica journal

(Editor's note: From turtles to toads to migratory birds, the rich ecosystem of this tiny Central American country is sending an early warning signal on how global warming is affecting animal life. Monitor contributor Moises Velasquez-Manoff set down his on-the-spot observations as he and Monitor photographer Andy Nelson traversed Costa Rica investigating the effects of climate change. A sample of those scribblings is collected here.)

May 12: Turtles nests and poachers

Today, Andy and I walked the beach with Emma Harrison, director of the Caribbean Conservation Corporation (CCC) in Costa Rica, which monitors sea turtle nesting at the Tortuguero National Park on the Caribbean coast. Every three days, the CCC conducts a census of recent turtle nests. Several species of sea turtle nest in Tortuguero's black, volcanic sands.

Right now, we're at the tail end of leatherback nesting season and the beginning of green turtle season. Leatherbacks, which have leathery dinosaurlike ridges running lengthwise down their backs instead of a hard shell, are the largest marine turtles, commonly weighing half a ton.

While the green turtle population has rebounded since conservation efforts began around the Caribbean, the leatherbacks have seen a slow but steady decline since the mid-1990s, when the CCC began counting.

We begin early on a bit of land just south of the national park. Rangers don't patrol here, so there's much more poaching. Jungle comes right up to the beach. Jaguars, which take the occasional nesting turtle, roam the seemingly impenetrable mess of trees, fronds, vines, and shrubs.

Crocodiles live in the brackish rivers that snake down to the coast here. There are even rumors of tapirs, South America's biggest land animal related to the horse and rhinoceros, sloshing about the lowland swamps.

It is an incredibly lush landscape, but at the mouth of the river where we begin our trek, piles of human trash greet us. Dolls' heads, plastic gallon containers, and many cheap flip-flop sandals are heaped on the beach. (For some reason, the majority of flip-flops are lefties – an enduring mystery, Emma says.)

Some of the trash washes up from the river that empties here, some floats in from neighboring countries in the Caribbean. It serves as a reminder of humanity's impact – intended or not – on the natural world, a kind of tangible parallel to the invisible heat-trapping gases spewing out of tailpipes and smokestacks thousands of miles away, but which nevertheless affect this place.

The beach becomes cleaner as we progress. We see 13 nests, many from the previous night. That's a good sign. But of those, eight have been poached. That's a bad sign. In Costa Rican culture, a myth endures that the eggs – often eaten raw – are an aphrodisiac. This drives much of the poaching business. But such a high percentage of poaches is not the norm, Emma says, calling it "heartbreaking."

The CCC educates the village children about the importance of the nests. But many poachers come from other areas during nesting season.

When facing such immediate threats, conservationists often can't begin to consider long-term threats like those posed by global warming, Emma says. If there are no turtles because the eggs have all been harvested, who cares about the potentially skewed sex ratios caused by a warmer climate?

And this speaks to what's fast becoming the mantra of our trip: The best way to prepare a species for the effects of global warming is to make sure the population is healthy and thriving: that it has the habitat and genetic diversity it needs to adapt and evolve to changing conditions.

May 13: When jungles spew carbon

Biologist Deborah Clark works in Costa Rica studying how tropical forests respond to fluctuations in climate.

Today as I talk with her during a break at a symposium on climate change's impact on La Selva Biological Station and Reserve, an old-growth jungle here, she says something rather profound:

In optimal conditions, a tropical forest absorbs carbon. Trees take it from the atmosphere in their photosynthetic processes. But trees also emit carbon when burning their energy stores, although it's normally a very small amount compared to what they're sucking up.

Here's the clincher: When it gets too hot – especially at night – the normally large gap between how much CO2 they produce and how much they remove from the atmosphere narrows. And when this happens, the tropical forest as a whole – emissions associated with the activity of fungi, insects, animals, and trees in the forest – may become a net producer of CO2.

In other words, if temperatures get too warm – especially night temperatures – tropical forests could begin exhaling vast amounts of carbon into the atmosphere, further heating the earth.

Long ignored, the tropics' response to climate needs more study, Dr. Clark says. So far studies here show that tropical forests indeed are quite sensitive to increasing temperatures.

The Arctic receives more attention both because the greatest temperature changes are predicted there and because, when there is change, it's easy to spot: The ice melts. Tropical systems, it's assumed, are somehow more resistant to change.

That's a false assumption, Clark says. Much has changed here over the past 30 years. Amphibians and reptiles are less numerous than they once were. Bird species have declined. Whether or not this is due to climate change is still unclear.

May 14: Dump data, save wildlife

Five days per month, Steven Whitfield, a PhD candidate at Florida International University, walks a staked-out plot of land in the old-growth jungle at La Selva Biological Station and Reserve in the lowlands of central Costa Rica.

He catches, measures, and marks the lizards or frogs he finds. It's hot, often raining, and always near 100 percent humidity. Ordinary pens and pencils stop writing. One has to have a special kind of paper, the scientists tell me, to write in these conditions – one that maintains friction. They have it. I don't.

But what's important – why we're here – are the long-term declines in both amphibian and reptile populations at La Selva.

After analyzing data spanning three decades, Mr. Whitfield and his colleagues have found that, much to their surprise, populations of those creatures are about one-quarter of what they were almost four decades ago.

Many hypotheses have been put forward as to why this is happening, global warming among them. But the analysis shows the importance of something else: keeping long-term records.

One hears this over and over again in discussions among the scientists here at La Selva – the importance of long-term studies and access to the work of previous scientists, both of which are crucial in catching gradual shifts driven by climate.

Yet sharing past research isn't automatic.

Someone joked that no one should be able to conduct studies here unless they make at least a 20-year commitment. But barring that, the scientists talk of creating a database open to everyone, where every researcher funded by a government grant will be required to "dump" his or her data, making it forever available to future researchers.

May 16: 'Seeing' the invisible

To be a science writer these days is to be intimately familiar with the number 380. It is the number of carbon dioxide molecules for every 1 million molecules of mostly nitrogen and oxygen blowing by in the air at any given moment. That's about a third more than the preindustrial CO2 level of 280 parts per million (ppm). And by century's end, the current 380 ppm is forecast to become 500.

With measurable shifts in climate and species already evident at 380, the vast majority of scientists say 500 is something to be avoided at all costs – unless we want to see much of Florida, Bangladesh, and New York City under water.

In other words, you could say that 380 is a celebrity of a number.

So imagine my surprise when, high above an old-growth jungle called La Selva ("the jungle" in Spanish), I saw 380 measured in real time.

We were near the top of a 132-foot tower made of aluminum tubing. The tower is part of an experiment measuring CO2 levels at different heights in the jungle. Measuring devices housed in white plastic boxes suck in small amounts of air and then beam it with a particular frequency of infrared radiation. Being a greenhouse gas, CO2 absorbs some of the radiation. A sensor records how much infrared makes it through the air sample. From the amount missing, a computer calculates the air's CO2 concentration.

Some 20 feet above the jungle canopy, with howler monkeys barking (they're very territorial and we were definitely in their territory), the CO2 level was jumping between 382 and 379 ppm.

I'd written the number many a time, bored people with it at parties, fretted over it, and explored its many disturbing ramifications.

But I'd never seen it. Perched on a tower dripping from the fine rain and vibrating with the easterly wind, I was "seeing" it – an invisible gas – for the first time.

In an instant, something I'd only known abstractly suddenly became concrete. Much of the so-called excess CO2 – about 100 of the 380 ppm – came from smokestacks and tailpipes thousands of miles away. And yet, 380 ppm was measurable here in a rain forest on the isthmus between North and South America, just as it was measurable in the US, China, Antarctica – anywhere on earth. What scientists call humanity's great experiment with climate change is not in a laboratory somewhere. It's right in front of us no matter where we go, surrounding us and filling our lungs with each breath. It is inescapable.

May 18: Ghosts of a foggy forest

We've come to Costa Rica to report on climate change because of the country's remarkable biodiversity and its notable conservation efforts, and, specifically, because scientists have documented mountain frogs disappearing at an alarming rate here.

Between 1987 and 1988 – a particularly warm year – two amphibians vanished from the forests of the Monteverde Cloud Forest Reserve in central Costa Rica.

The golden toad and the Monteverde harlequin frog haven't been seen since. Alan Pounds, scientist-in-residence at Monteverde, calls it the first known extinction due, at least in part, to climate change.

The irony is that we've traveled some 3,000 miles to report on species that no longer exists. We've come to see the hole left by something gone forever.

So in some sense, a visit to Monteverde is like a visit to an old, beautiful, but deserted castle. You can imagine what the inhabitants looked like – how they clustered in the puddles beneath the trees – but it's just an exercise in visualization based on stories from those who were witnesses. The inhabitants themselves are history.

These foggy, dripping heights were the only spot on earth where the golden toad existed. In the tropics, species that evolve on mountaintops are often limited to a single mountain or mountain range. The hot lowlands represent an impenetrable barrier to moving elsewhere.

And when climatic conditions change or disease invades, there are no rafts for them to hop aboard. They can't sail to another mountaintop. Besides, more often than not, the other mountaintops will have their own native species, and these species will have their own problems.

Remove a brick from a wall, and it leaves a hole. Likewise, take a species out of an ecosystem, and there's a gap. The whole structure, which humans inevitably rely on in some form or another, grows weaker, moving ever closer to collapse.

That hasn't happened at Monteverde – yet. But there is much evidence of a system in flux.

Some bird species have moved up the slope from the lowlands. Others, already at the top of their range in terms of temperature, have nowhere else to go, and seem to be growing scarcer. With the disappearance of so many amphibians, Dr. Pounds says he thinks birds may be having a difficult time getting enough protein.

For what it's worth, during the three or four hours we spend at Monteverde, we see nary a lizard or frog.