Global Warming Facts and Questions

There are many authoritative sources of information about climate change. Among the ones I recommend are: the new FAQ from the The Australian Academy of Sciences, the book, The Science and Politics of Global Climate Change; the blog,; the journal, New Scientist; entries in Wikipedia; and position statements from the American Geophysical Union and the American Meteorological Society.

For an overview, here is an FAQ that succinctly addresses the questions I hear from non-experts about climate change. Following this are my recommendations for actions that citizens and nations can take to counter global warming. Let me know what you think.

Is "global warming" really happening?

No question.

Every global indicator shows warming: three independent instrumental networks; sea ice (retreating); permafrost and glaciers (melting); species migrations (poleward); borehole and tree-ring-derived temperatures (upward); and spring thaws (earlier). And don't forget underwear...

The warming has varied regionally, but the global average temperature now is about 0.7 degrees celcius warmer than it was 100 years ago and probably the warmest in at least a millenium [NRC 2006]. Europe and Northern Asia have warmed more than the US or Australi??a, and the Arctic the most, enough to significantly affect indigenous peoples and wildlife.

Is recent, weird weather due to climate change?

Weird weather happens - always has, always will.

The media love to dwell on it, making it seem worse than it is. No one event can be blamed on any particular culprit. But some aspects of the weather (see below) are getting a boost from climate change.

Is "An Inconvenient Truth" accurate?

There are exaggerations in this movie, but in my view the main messages are important and on target.

"An Inconvenient Truth" attributes increased tornadoes, disease, and insurance payouts to recent climate change, which I'm pretty sure is wrong. Cooler heads say the true causes are, respectively: better detection of weather extremes; increasing population density and air travel; and more at-risk property being built. Also Gore was criticised for showing the inundation of Florida without noting that this is expected to take at least two centuries to happen. But the other impacts of climate change cited in this movie are real, and I expect more serious ones are lurking over the horizon.

What about the tropical cyclones? Are they getting worse because of global warming?

The jury is out on this particular question.

Most climate scientists agree that warming must—other things being equal—slightly increase the maximum cyclone strengths. But that comes nowhere near explaining the near-doubling of US Atlantic hurricane activity in recent years. Some of my colleagues argue that global warming is responsible for that, but the evidence is ambiguous and it's unexplainable by current theory, so I wouldn't tell Floridians to sell their coastal property just yet. A number of recent studies have cast further doubt on whether hurricane intensity or frequency increases will be all that severe. My guess is it'll be many more hurricane seasons before this is settled.

What about the ozone hole? Is that causing climate change?

No, that's a separate problem.

This issue was successfully addressed through an international agreement to phase out freon-type gases once used in refrigerators, air conditioners and spray cans.

Don't temperatures swing naturally?

Of course, but as far as we can tell this can't explain recent behavior.

We are rapidly learning more about past climate changes from examination of geologic evidence, which is probably the most exciting field in climate science today. Some changes have been huge: 55 million years ago the north pole was as warm as Brisbane is today, while 20 thousand years ago, much of North America was under miles of ice. The really warm climates all occurred long before the advent of upright primates, but prehistoric humans made it through some pretty cold times. Since the advent of agriculture, climate has been relatively boring.

Science is a process of testing hypotheses against evidence. Many scientists, using different methods, have tested the hypothesis that the recent warming is also a natural shift. Every analysis has yielded the same answer: No—the warming since 1970 has been too widespread and too rapid. A few scientists still reserve judgment on this, but no model has been able to explain the warming naturally. Mountain ice and polar ice shelves that are thousands of years old are melting, which would be an amazing coincidence if humans weren't involved.

So what's causing this?

The burning of fossil fuels is the biggest contributor.

Scientists have predicted for over 100 years (see history of the science) that burning fossil fuels would warm the planet by adding to the atmosphere significant amounts of carbon dioxide, a so-called "greenhouse gas" that absorbs infrared radiation, inhibiting planetary cooling. This affect is observed by satellite. Greenhouse gases are naturally present (we all exhale carbon dioxide, for starters), and without them we'd all freeze, but by burning fossil fuels to power our cars and factories, we've added a lot more to the atmosphere. The importance of greeenhouse gases in influencing a planet's climate is supported by Earth's geologic record and by comparing the climates of Earth, Mars and Venus. The only question is exactly how sensitive our climate is to them.

We try to calculate this from known physical laws. Over the last four decades these calculations have grown pretty complicated, predicting more details like cloud cover and type, for example. That hasn't changed the answers much. Every calculation has predicted a substantial warming (generally betweeen 2 and 5 C globally) if atmospheric carbon dioxide is doubled from 0.028% to 0.056% of the atmosphere by volume. It's currently 0.038% and climbing fast. Human activities are also adding other greenhouse gases like methane and nitrous oxide, but carbon dioxide is the most important.

Natural factors like volcanic eruptions, shifts in ocean currents, and fluctuations in solar luminosity have been important in driving small climate changes over the past few millenia, but have not increased in recent decades. Human air pollution (the kind that causes acid rain) is also important. Ironically, it counteracted part of the greenhouse warming during the 20th century, but is doing so less now due to pollution controls (and would be unable to keep up even if we went back to the bad old, dirty days). Deforestation and agriculture also affect local climate as well as releasing additional greenhouse gases.

The key thing is that we are hitting the climate system harder than any known natural forces. That's true regardless of uncertainties in how the climate system responds. And the recent warming is right in line with long-standing predictions (for example, it has since tracked the predictions published by the IPCC - the Intergovernmental Panel on Climate Change - in 1990).

Are we sure carbon dioxide is actually rising, and that burning fossil fuels is the cause?


We now have very accurate histories showing little change for millenia, then a meteoric rise after coal came into wide use in the early nineteenth century. Carbon-14 measurements also confirm that the added gas comes from ancient fossil fuels. Other greenhouse gases like methane followed a similar trajectory, though their sources are more complicated.

Doesn't carbon dioxide have good effects, too?

Without any CO2 we'd indeed be in trouble, but the consequences of adding a lot more to the atmosphere are generally not good.

CO2 is poisonous to humans, but not at concentrations that we could ever create globally.

It forms carbonic acid when dissoved in water, which is making the oceans more acidic. This already appears to be harming corals; these and other organisms at the base of the ocean food chain will find it harder to build shells. This consequence may be as serious as climate change, but isn't getting the same attention, in part because it is less controversial (did you realise the more agreement there is among experts, the less you'll hear about it?).

Finally, carbon dioxide helps plants grow, but not necessarily the ones we want (one of the biggest beneficiaries, evidently, is poison ivy! This and other vines are taking over some forests). Also, the extra growth comes at the expense of lower nutritive value, so it isn't clear that more CO2 will be helpful from a food point of view.

Could plants absorb the extra carbon dioxide?

They are absorbing some—otherwise atmospheric amounts would be rising even faster.

Studies of "carbon fertilization" of plants (the potential increase of a given plant's uptake of CO2 when there is more in the air) have shown a limited impact over time, so to increase plant uptake significantly would require more plants. Widespread forest planting would help, but only enough to delay warming by maybe a decade or so, and only so long as there are no other competing demands for the land. Unfortunately, future warming will probably work against us by causing soils to start releasing stored CO2.

Should we be concerned about a warming of one little degree?

Here are four reasons why we should:

1) This is only the tip of the iceberg. If we burn through most of Earth's fossil fuels we could quadruple atmospheric carbon dioxide, causing an estimated global mean temperature rise of 4-9 C. We could easily do this in less than 200 years even if energy consumption stopped increasing. Also, even if we ceased all burning immediately, another degree C or so of warming is "in the pipeline" from past emissions.

2) It isn't just the heat, it's the humidity! A 3C warming causes about a 25% increase in absolute humidity. This would make each summer heat wave feel at least 6C hotter (to a warm-blooded creature, which I assume includes most readers).

3) Most of the life on Earth lives "on the edge." 1C is enough to bleach corals, for example. A tree, animal, or skier has to move about 150 km poleward for each degree of warming to maintain the same climate envelope. At current warming rates this is about 5 km per year, which is impossible for most plant species, so forests will get left in the dust.

4) Other things besides temperature and humidity will be affected (see next question).

How will a warming climate affect us?

Milder winters and hotter summers are just the most obvious effects.

Uncertainty and debate on this subject continue, but large climate changes will surely be disruptive, as we have spent thousands of years fine-tuning our activities and infrastructure to the current climate (like producing wine in South Australia, much of which will become untenable with a few degrees' warming).

In addition to milder winters and hotter summers we have good reason to expect:

  • Longer growing seasons (good for farming)
  • Less snow and more rain (very bad for summertime water supplies in much of the world, including Australia)
  • Less reliable, but heavier rains (bad for farming and flood control)
  • Shifting storm tracks (bad for southern Australia, New Zealand, Chile, Argentina, and probably sub-Saharan Africa)
  • Failing health of old-growth forests and other ecosystems
  • Rising sea levels and displaced coastal populations
  • The Unexpected
Many other impacts are possible but these are the ones that are both theoretically predicted and observed to be under way now (except the last one, but it's the most certain of all!). Impact severity is expected to scale with the square of the amount of warming. In other words, a little climate change isn't so bad, but a lot is. Cooling wouldn't be good either; all life on Earth is finely tuned to the current climate.

Isn't there scientific disagreement over any of this?

The legitimate disagreements are over details.

All reputable scientists, even outspoken "climate-change sceptics" acknowledge that we have caused greenhouse warming and it will continue. Scientific uncertainty and/or dispute are limited to the severity of future changes, and the extent to which certain recent trends (like the loss of the snows of Kilimanjaro) are attributable to greenhouse gases. These are obviously important matters but not the same as disagreeing about the fundamental nature of the problem. There are quacks - and the odd scientist person who ventures outside his or her area of expertise - who will publicly dispute even the basic points. Unfortunately some groups invested in the status quo have run disinformation campaigns to confuse the public. Disagreements are highlighted by the media, and quacks given a dismaying amount of attention, while concensus is too dull to report.

A few of my colleagues claim that model predictions of future warming are excessive. They have no calculations to back this up, and in my view their claims have no valid scientific foundation - though they can't be proven wrong per se until warming is fully realised.

Past contrarians whose ideas were initially rejected but turned out to be right, like Alfred Wegener and others who proposed the theory of plate tectonics, typically had a new theory that explained data better than the prevailing wisdom. They were often outsiders. Their new theories made the reigning scientific "chiefs" look bad and challenged deeply ingrained notions, so only when the chiefs died off did the new theories enter the mainstream. That description does not fit today's climate "contrarians": they have no new theory, they only criticize well-tested existing theory (and win lots of attention). Support for their views has steadily eroded (in the 1960's most scientists were skeptical about any theory on climate) and is essentially non-existent among the youngest generation of scientists.

Aren't scientists a special-interest group? Weren't they warning of global cooling once? Are they scaring us to get more research funding?

This may sound reasonable until you learn a bit more.

For one thing, scientists aren't exactly the most...uh...organised people. But seriously, this conspiracy theory is riddled with holes.

Scientists get rewarded by (a) being right in the end, (b) bucking the conventional wisdom (subject to (a)). It doesn't pay to jump on bandwagons, because whoever started the bandwagon will get the credit. And it's worse if they're headed in the wrong direction.

Prior to the 1970's there was definitely no documented "consensus" on any theory of climate, analogous to that articulated today -- despite what some will imply as they hold up "global cooling" articles from old issues of Life magazine or Readers' Digest.

Atmospheric scientists have always known that fossil fuel burning would eventually cause warming, though the relative importance of this emerged gradually (see Spencer Weart's excellent history of the science). Articles in the scientific literature have consistently said this even during the cooling of the 1960's.

Is this something we'll just have to live with? Wouldn't taking real action destroy the economy?

No. Economists calculate that stabilising atmospheric carbon dioxide concentration at a safe level (low enough to avoid the most serious impacts) can be done by spending only a few percent of global GDP. This is equivalent to delaying economic growth by a few years so that, for example, per-capita wealth that would have been attained in 2030 is not attained until 2033.

Quantifying the economic impact of climate change if we don't change course is quite difficult, and estimates (more uncharitably, guesses) range considerably. Some economists say don't worry. My guess is that we will be surprised and that these surprises could be far, far nastier than a few percent loss of GDP.

"Ask yourself one question: 'Do I feel lucky?'" -- Dirty Harry

Should we act now, do we have time to "wait and see", or is it already too late?

It is too late to prevent some more climate change in the next few decades, but not too late to forestall severe consequences for our grandchildren and many generations after them; many now see the key goal as keeping the warming to less than about 2C above historical levels. Among other things, this should prevent the eventual melting of Greenland. I do advocate "wait and see": wait and see what kind of technologies we can develop before we build any more old-fashioned infrastructure!

Many nations, especially India and China, are gearing up to rapidly expand their electricity-generating and fuel refining capacity, and they are mostly sticking with old, polluting 20th-century technology. This is a looming disaster, committing us to a huge, additional belch of greenhouse gases over the next few decades that would more than double our previous emissions and guarantee more serious impacts down the road. Now is a pivotal time in world history.

The point is that we are already "acting" by building more stuff. And since we'll never know exactly what climate change will bring until it's far too late, waiting for "better science" is a de facto decision to give up.

Technological progress is the key but only happens when spurred by markets or government mandates. Meanwhile, gases are building up relatively rapidly, and removing them from the atmosphere (though technically feasible) will probably remain impractical. Geoengineering to counteract climate change could help, but might not go as planned, would have to be maintained by our descendants for centuries, and would not address the non-climatic effects of CO2. There are a few "no regrets" actions that would have economic or health benefits even in the absence of a climate problem (like eliminating subsidies that now prejudice us toward fossil fuel use, or pursuing more sensible coastal development policies). These would at least get us started.

Ultimately, to achieve meaningful reductions in emissions would require some combination of wholesale shifts to nuclear power, massive increases in energy efficiency, or capture and storage of carbon dioxide before it reaches the atmosphere (check this out—it may be our best option).

What can I do?

Each of us can help through our personal decisions and our political voices.

The "green" impulse is to conserve energy. Unfortunately this will do little by itself to improve climate. It does however have two very important, indirect benefits:

  • Oil conservation aids the economies and national security of oil-importing nations, by relaxing price pressures and reducing the huge flow of capital out of the country to nations that spend it unprofitably for us (the list of "friendly" countries that export oil is getting pretty short unless you really stretch your definition of friendly, and oil revenues continue to be the perfect tonic for sustaining authoritarian regimes). In the not-too-distant future we'll have to make do with less oil no matter what, and the sooner we start adjusting, the easier it will be.
  • Electricity and fuel conservation will postpone the need for new generating and refining capacity. This buys us a little time to work out the best new designs before building new power plants and oil refineries.
Of course we could just wait until high prices force us into conservation, which must happen sooner or later. But then we forego both of these benefits. New technologies develop and deploy only when a market exists or when society decides to make it happen.

"The time to repair a roof is when the sun is shining."--John F. Kennedy

Politicians are finally talking about climate change: listen carefully to their proposed solutions. Subsidizing new technologies is popular because it doesn't involve any tangible sacrifice. This may be helpful, depending on what is being subsidized. But plenty of energy-saving technologies have already been developed (many after the 1970's oil shocks) and have been gathering dust on the shelf. The market isn't demanding them because consumers are not individually rewarded for adopting them, or for simply using less fossil fuel.

What you and I can do:

  • Talk about this problem with friends and raise it with elected representatives. This is the only way to get and keep it on the national agenda, where it belongs. Push for policies that reward individuals and companies appropriately for reducing their emissions. If possible, force your politicians to take a position on specific and effective actions (here is one example from climate scientist Jim Hansen) rather than simply issuing toothless edicts.
  • Adopt energy efficiency as a key criterion in choosing what to buy and where, and tell the stores and manufacturers that we're doing so. This includes cars, appliances, and investments. We exert more power through our wallets than our ballots. Actively consider new technologies that look helpful even (or, especially) if they are unfamiliar.
  • Turn down the A/C (I know...very unpopular). This daytime energy hog is the biggest driver for generating capacity, and it's something humans (including most alive today) once managed to live without. Air conditioning has even been implicated in obesity. If we shop or work in over-cooled places, let's complain! It may even stave off a few colds or Legionnaire's disease.
  • Try to get our kids interested in science (or, if you are a kid, or behave like one, get interested yourself!). Scientific ignorance is an important part of this and many other big problems (for example, in the US in 2005, the New Orleans levee system failed in part because engineers had been overruled by un-savvy bureaucrats during the levee's construction).

What can we do as a country?

Here's an idea I like, that should not offend anyone's ideological stance: a product-labelling program that would tell the buyer the amount of carbon dioxide that was emitted in making and transporting every product or service. Here's an easy one: each litre of petrol burned in a car engine puts over two kilos of carbon dioxide into the atmosphere. Supermarkets in Britain and France are starting to do this for a few food products, due to customer demand for it. It's a bit like the nutrition labels we now have on foods, supposedly to help us be healthier. But carbon labels would work a lot better: while we don't really know what makes us fat (it's more complicated than just eating too many calories or too much fat), we do know what will cause global warming. And let's face it, we already know that a cup of butter has a lot more fat in it than a cup of milk, but do you know how much oil is required to put a bunch of bananas on your table? Me neither. We need to find out.