No global cooling in Cosmos

July 25, 2011

A while back I started watching the famous documentary series `Cosmos’ by Carl Sagan. The series is very good, although it might take you more than the first episode to appreciate that if you see it today -you’ll have to get past that voice, droning on like reverend Lovejoy from the Simpsons and that ridiculous spaceship that William Shatner wouldn’t be caught dead in. But after a while, Sagan’s voice-over improves and he all but abandons his spaceship to end up presenting a series of fascinating lectures, supported by (mostly) excellent multi-media support.

Global cooling?

Being an astrophysicist myself, most of the science isn’t new to me (some of it is even slightly outdated) and I enjoy the series mostly for the cultural references and historical context. But then something caught my eye in episode 4 when the discussion turned to climate change. You might remember the but in the seventies, it used to be global cooling! meme that has been spread vigorously by fossil-fuel industry funded stooges (e.g. here, unmasked here) or by pop science writers who are really not all that clever. The purpose of the meme is of course to obfuscate and to lead the non-expert to believe that scientific consensus on climate change has been swinging back and forth between wildly diverging opinions over the course of the past decades, thereby diminishing the impact of the current overwhelming consensus in the climate science community that global warming is real, occurring now and is man-made. The whole global cooling story has already been thoroughly debunked (e.g. here, here). Since Cosmos was originally broadcasted in 1980, closer to the global cooling craze than the global warming craze, had the former really existed, it is interesting to hear what Sagan has to tell us about global climate change, if only to as a reminder how scientific consensus actually did emerge over the past decades.

Cosmos, 1980

The destruction of trees and grasslands makes the surface of the Earth brighter. It reflects more sunlight back to space and cools our planet. After we discovered fire we began to incinerate forests intentionally to clear the land by a process called “slash and burn” agriculture. And today, forests and grasslands are being destroyed frivolously, carelessly by humans who are heedless of the beauty of our cousins the trees and ignorant of the possible climatic catastrophes which large-scale burning of forests may bring.

So is Sagan implying here that we should be afraid of global cooling? At least he gives us a concise description of the mechanism. (By the way, the reference to trees as cousins should not be read as some wishy-washy new-ageism, but as a reference to an earlier point in the series where the incredible similarities on chemical and DNA level across the different species were discussed).

The indiscriminate destruction of vegetation may alter the global climate in ways that no scientist can yet predict. It has already deadened large patches of the Earth’s life-supporting skin. And yet, we ravage the Earth at an accelerated pace as if it belonged to this one generation, as if it were ours to do with as we please. The Earth has mechanisms to cleanse itself, to neutralize the toxic substances in its system. But these mechanisms work|only up to a point. Beyond some critical threshold, they break down. The damage becomes irreversible. [..] The bright, sandy surface and dusty atmosphere of Mars reflect enough sunlight back to space to cool the planet freezing out all its water, locking it in a perpetual ice age.
Human activities brighten our landscape and our atmosphere.
Might this ultimately make an ice age here?

Although the specter of global cooling is indeed raised, so is the lack of scientific certainty and consensus… But what about the greenhouse effect and the state of climate science in 1980?

At the same time, we are releasing vast quantities of carbon dioxide, increasing the greenhouse effect. The Earth need not resemble Venus very closely for it to become barren and lifeless. It may not take much to destabilize the Earth’s climate to convert this heaven, our only home in the cosmos into a kind of hell. The study of the global climate, the sun’s influence, the comparison of the Earth with other worlds… These are subjects in their earliest stages of development. They are funded poorly and grudgingly. Meanwhile, we continue to load the Earth’s atmosphere with materials about whose long-term influence we are almost entirely ignorant.

As I said, no consensus. And rather than revile today’s state of climate science, for example as summarized in the IPCC reports, we should be impressed with how far we’ve come in only a few decades.

Cosmos, 1990

Already ten years after the first airing of Cosmos, climate science (as well as astronomy) had advanced considerably, and when the series was reissued in the early nineties, a brief update was appended to many episodes. Regarding climate change, a ten year older Carl Sagan now had the following to add:

Since this series was first broadcast the dangers of the increasing greenhouse effect have become much more clear. We burn fossil fuels, like coal and gas and petroleum, putting more carbon dioxide into the atmosphere and thereby heating the Earth. The hellish conditions on Venus are a reminder that this is serious business. Computer models that successfully explain the climates of other planets predict the deaths of forests, parched croplands, the flooding of coastal cities, environmental refugees, widespread disasters in the next century unless we change our ways.


The surface of Venus (from Cosmos episode 4)

Just to dwell on the obvious… Sagan’s future is today’s now. We currently are experiencing many of the gloomy predictions from twenty years ago. I wrote this in NYC during a record shattering heat wave across the U.S. 71% of Texas suffers from exceptional drought, its driest period there since 1895, with heat waves raging through many southern states… The worst drought in Somalia in 60 years… One fifth of Pakistan flooded last year… Enormous floods in China and Australia as well… a monster heat wave in Russia… a drop in September arctic ice volume from 10,000 cubic km in 1980 to 4,000 cubic km now. The list goes on and on… Sagan wouldn’t mince words were he to provide another update to Cosmos!

What’s in it for me?

March 12, 2011

you maniacs!

Global temperature

The effects of global warming are visible all over the world, but not all evidently so. For example, the rise in global mean land-ocean surface temperature has been 0.6 degrees Celsius since 1980. But no one experiences the global average temperature directly -it is after all the average over a wide range of temperatures from cold Siberia to the Sahara desert, so in terms of personal experience this fact is meaningless.

One needs to know the context in order to understand what this means. This context is provided by facts such as that this change is roughly twice the global mean temperature change between 1880-1980, that the uncertainty estimate for recent data is 0.1 deg, that temperature reconstructions reveal the current temperature to be unprecedented over at least 1800 years, etc.

Single events

There already have been colossal changes and events in recent years with a clear and obvious impact. There is the incredible drop in arctic ice volume (11,000 cubic km since 1980, with only 4,000 cubic km left on average in sept. 2010, again context is needed). Or the recent flood in Pakistan that affected an area at least the size of England. And other floods, like the flash floods in North-West China (resulting in over a thousand deaths) or the big flood in Australia (which affected 200,000 people). But the link between events like floods and heat waves and global warming is a tricky one, just like the link between smoking and lung cancer in an individual patient: the increase in their occurrence is a solid prediction in a statistical sense, but the story for each individual case is complex. Last year’s heat wave in Russia is a case in point, and may to a large extent be attributable to a `normal’ weather extreme [update Mar 14, 2011: or global warming after all? See here for a compelling argument]. Besides, all this still doesn’t directly touch upon the lives of people here in America -who typically haven’t visited the Arctic recently, let alone twice and know in their hearts that countries like Pakistan don’t really exist. Even the rising global food prices, caused mainly by weather calamities and stirring up mass protests and revolt in the Arab world, such as the revolution in Egypt, have little impact in the U.S. as Americans spend a relatively small fraction of their income on food. Only when global warming and weather start to impact the rental prices here in New York I’m going to be seriously screwed.

Global warming predictions for New York

All this raises a question: what will we experience locally from the global climate change? The simple rule of thumb answer -expect more extreme weather events as the temperature erratically becomes higher and higher- is just that, a rule of thumb. It tells us that the U.S. snowstorms last winter are consistent with and expected from global warming, but the more local you look, to more complicated everything becomes. A very useful resource is the report Global Climate Change Impacts in the United States by the United States Global Change Research Program, available here.

Image from page 109 of "Global Climate Change Impacts in the United States"

When it comes to New York (or the North East coast in general), it tells us the following. First, the past:

Since 1970, the annual average temperature in the Northeast has increased by 2°F [=1.1 deg. Celsius], with winter temperatures rising twice this much. Warming has resulted in many other climate-related changes, including:

  • More frequent days with temperatures above 90°F
  • A longer growing season
  • Increased heavy precipitation
  • Less winter precipitation falling as snow and more as rain
  • Reduced snowpack
  • Earlier breakup of winter ice on lakes and rivers
  • Earlier spring snowmelt resulting in earlier peak river flows
  • Rising sea surface temperatures and sea level

Then, the future:

Over the next several decades, temperatures in the Northeast are projected to rise an additional 2.5 to 4°F in winter and 1.5 to 3.5°F in summer. By mid-century and beyond, however, today’s emissions choices would generate starkly different climate futures; the lower the emissions, the smaller the climatic changes and resulting impacts. By late this century, under a higher emissions scenario:

  • Winters in the Northeast are projected to be much shorter with fewer cold days and more precipitation.
  • The length of the winter snow season would be cut in half across northern New York, Vermont, New
    Hampshire, and Maine, and reduced to a week or two in southern parts of the region.
  • Cities that today experience few days above 100°F each summer would average 20 such days per summer, while certain cities, such as Hartford and Philadelphia, would average nearly 30 days over 100°F.
  • Short-term (one- to three-month) droughts are projected to occur as frequently as once each summer in
    the Catskill and Adirondack Mountains, and across the New England states.
  • Hot summer conditions would arrive three weeks earlier and last three weeks longer into the fall.
  • Sea level in this region is projected to rise more than the global average,

So, what’s in it for me? (sang the N.Y. Indie band the Walkmen in 2004). The bottom line, if you’re planning on doing business or living in NY, you’d better start paying attention:

The densely populated coasts of the Northeast face substantial increases in the extent and frequency of storm surge, coastal flooding, erosion, property damage, and loss of wetlands. New York state alone has more than $2.3 trillion in insured coastal property. Much of this coastline is exceptionally vulnerable to sea-level rise and related impacts. Some major insurers have withdrawn coverage from thousands of homeowners in coastal areas of the Northeast, including New York City.

Rising sea level is projected to increase the frequency and severity of damaging storm surges and flooding. Under a higher emissions scenario, what is now considered a once-in-a-century coastal flood in New York City is projected to occur at least twice as often by mid-century, and 10 times as often (or once per decade on average) by late this century. With a lower emissions scenario, today’s 100-year flood is projected to occur once every 22 years on average by late this century.