We live on a ball of rock.

Nothing holds it up.

Nothing needs to.

Its place in the universe is due to the star that gave it birth, the centre of its orbit, and the source of its heat and light until the end of time.

The Problem

We humans are the most successful, the cleverest and most adaptable and widespread species on Earth, by a very big margin. Today, we absolutely dominate the biosphere in a way no other species has done, at least for a half-billion years, occupying or exploiting most of its ecological space.

Converting the complex living surface of the planet into a human environment rather suddenly (in a couple of centuries) has had some unintended consequences.

This is one of them:

The slow rise in the concentration of carbon dioxide in Earth's atmosphere over our "prehistoric" period - 8,000 years or so - followed by an extraordinary fast rise in the last 100 years.

The measurements were made on air trapped inside glacial ice, and are quite accurate ... you can see the range of estimates from several different Antarctic sites. Since 1958 CO2 has been monitored directly in the atmosphere with great precision.

CO2 rose about 15 parts per million by volume (ppmv) from its interglacial value of about 265 ppmv until about 1900. Since then it shot up more than 100 ppmv. It will pass 400 ppmv sometime in the year 2016 - something not seen on Earth for at least 3 million years.

Unless you have the right scientific background, this problem isn't particularly easy to understand ... but understand it we must, if we are to be any use to our grandkids. In the rest of this site, I'll try to explain it in some more detail, and show you what these kids would want us to do, if they were old enough to advocate for themselves.

On the next page I try to untangle the reasons why we are in this predicament.

This helps us to think clearly about what we have to do to fix it.

Here is something else that's accompanied human success:

The record of global mean surface temperature for the last 11,000 years ... the Holocene epoch - all of human civilization. The pink line shows the mean of estimates used to compile the record; the grey band shows the range of uncertainty for the ensemble. Zero on this scale is the mean temperature for the interval 1961-1990.

These ancient temperatures are detected in various places - old corals, tree-rings, cave stalagmites, lake floor sediments, and ice - using precise radio-chemical methods. The very steep pink line at the right is the 20th century, which is measured of course, with meteorological thermometers.

After reaching a warm plateau 8,000 years ago, the Holocene has been slowly cooling. In the last 100 years, that cooling has been reversed, and the world's temperature is climbing very steeply, compared with the natural rate of change.

These two changes in physical conditions on Earth are related. In fact, some scientists anticipated them a century ago. The way the gas affects temperature is understood very thoroughly. A few investigators even think they can detect a human influence on the atmosphere as long ago as 8,000 years, when forest clearance and rice cultivation got going in a big way (you can see this gradual rise on the first graph). Be that as it may, our alteration of the Earth’s surface systems in the last 150 years is unmistakable. Today, human activity adds to the air more than 100 times as much CO2 as all the world’s volcanoes do in an average year. The rise in CO2 concentration in the last 50 years has been about 200 times faster than it was at the end of the ice-age (which is the quickest natural change we know in detail). For better or worse, humans are a geological force, and quite capable of changing the state of the planet’s surface profoundly.

But, you might object, CO2 is a very minor component of the atmosphere (about 1 molecule in 2,500) - so what’s the big deal? Why does a smallish change in its abundance start to warm the surface? And is a degree or two of warming a bad thing? Couldn’t we just adapt to it?

This takes us to the heart of the matter. The problem we’ve inadvertently caused is not really about a bit of warming in the air, it’s about a change in the whole energy budget of the planet - the balance of incoming and outgoing energy flow that determines how hot it is here. That’s what we need to focus on to understand this problem.

Earth’s energy balance

Belonging in the solar system, Earth is warmed by the Sun. In fact 99.97% of all the energy on our planet’s surface is sunlight. It rains down on us continuously at the end of its 150,000,000 km journey; it’s stored in heat reservoirs - the land and the air, but especially the ocean - and it is held in the biosphere, in the form of chemical (metabolic) energy - sunshine captured by plants and everything that eats them.

Earth, like everything else in the cosmos, exists in space, and if it were not for the Sun, we’d be as cold as space - minus 270℃. According to the laws of physics, everything that has an energy income must expend energy. If a system has been around long enough, and the income is steady, like Earth’s radiation by the Sun, then the output and the resulting equilibrium temperature will be steady too. If either income or expenditure change, temperature will change accordingly - whether fast or slow depends on what kind of system it is - but the surface temperature (where energy exchanges happen) is always determined by the energy balance.

The Earth's energy balance

Virtually all Earth's energy comes from the Sun. All Earth's radiation goes to space. But energy doesn't simply escape from the surface to space, the way it does on the Moon. Something interesting happens right next to the planetary surface. A lot of heat is transferred to and from the air, ocean & land; and lots of it circulates in the air (those fat pink arrows show how much).

In fact, a warm layer of air next to the solid surface is an essential feature of life on Earth. It's just as if our planet had a blanket  all over it, holding heat beneath. The numbers give you an idea how powerful this (greenhouse) effect is.

It turns out, the strength of the atmospheric greenhouse depends precisely on the amount of CO2 in the air. This trace gas is the planet's "thermostat".

What happens if the energy balance changes?

If the Sun were to shine more brightly from tomorrow, Earth would begin warming, and also radiating away more energy until, after some time, the energy loss was again equal to the income. As long as this new balance lasted, the surface would be warmer. The same would happen if for some reason, Earth’s energy expenditure were reduced … the surface would warm and radiation losses would increase until, after some time, they matched the solar income. The warmth would be permanent as long as this balance lasted.

That is, in fact what has happened. The CO2 we put into the air all the time when we burn coal, oil & gas, cut and burn forests, plough the soil and make cement; and the methane we put there by raising livestock and growing rice; the nitrous oxide from vehicle exhausts and fertilizers - all these gases have the effect of reducing Earth’s radiation losses, trapping extra heat in the lower atmosphere. So much heat has been trapped this way in the last century or so that, if it had all stayed there, the near-surface air temperature recorded by weather thermometers would have risen by 36℃ - more than enough to extinguish all life on Earth. Luckily for us, the atmosphere doesn’t store much heat - nearly all the extra warmth passes from the air into the ocean. It’s going in there at a rate equal to the energy of 400,000 Hiroshima atomic bombs every day!

This is how much the amount of Sunlight reaching Earth varies in the course of normal solar cycles ... about 0.1%.

The modern CO2 rise and the increased atmospheric water vapour that comes with it, together exert an effect on the energy balance more than ten times greater than this. Current warming is not due to the Sun.

What happens to energy accumulating on Earth's surface?

If this prodigious amount of extra energy isn't all heating the air, where is it?

It's mostly in the ocean. The global ocean acts as Earth's heat reservoir - over 90% of the added energy goes in there. Heat is trapped in the lower atmosphere by extra CO2 and water vapour, then pretty quickly transferred to the sea at the interface of wind and waves.

Water doesn’t heat up nearly as much as air when energy is added, so the ocean can soak up the accumulated heat easily. But it doesn’t disappear, and sooner or later it will all be spread around, warming every part of the surface, including the great polar ice sheets. This takes a while - centuries in fact - so all the effects of adding energy to the surface systems can appear almost invisible to us, and still cause enormous problems for our descendants hundreds and thousands of years in the future.

The problem therefore has two faces - it’s an accidental result of economic activity, and also a great injustice to the people of the future, starting with our children and grandchildren, but extending for countless generations to billions of people we will never know. It just happens to be insidious (you need scientists to tell you, otherwise you’d never know) and sluggish (it will take many centuries to develop its full effects), so we don’t find it very frightening. It also brings bad news for everyone who benefits from our use of fossil fuels (just about all of us) and extra bad news for the companies that extract and sell those fuels. Together, they are the biggest business on Earth by a long way. Quite naturally, they have resisted the idea that their products are planetary poison.

Political systems are human inventions designed to help us sort out matters between competing interests. But this is a case where all of us are in the same boat. The citizens of the world and our fellow creatures are up against the laws of physics. We can’t negotiate this, we have to take the best advice our experts can give, and do what needs to be done. And yet our political leaders still seem to want to treat it it as if it were an ordinary political or economic problem - with lots and lots of talking but very little action.

We’ve been behaving just as if we don’t know what we certainly do know.

The problem in a nutshell:

The atmosphere contained about 1,600 billion tonnes of carbon dioxide in the year 1800; humans have added  ⅔ as much since ... most of it in the last 50 years.

Natural processes will eventually incorporate this carbon into Earth’s carbon cycles ... but over 100,000 years or more - not nearly fast enough for us.

Meantime it will get hotter & hotter. The time to fix this is now ... as fast as we can.

Any change in surface reflection or transmission of energy through the atmosphere must affect the temperature on Earth

Some people have said we shouldn’t be too concerned

Many Russians, for example have taken the view that their cold country stands to benefit from expanded agriculture and access to minerals in the Arctic (and a shorter, warmer winter). But in the summer of 2010 these thoughts were given a sharp corrective by the worst heat wave and drought ever, accompanied by ferocious fires and massive crop losses. A recent study by Stefan Rahmstorf and his colleagues addressed the question: how probable would this event have been without twentieth century warming? Their answer: the likelihood of such an unusual summer has risen five-fold due to extra greenhouse gases.

Another study of the terrible European heat

wave of 2003 found that, on current trends, a

summer at least as bad as that would occur

every second year by 2030 - and would be an

unusually cool one by 2060.

The fact is, there will be a few winners in a

warmer world - but overall, the damage to

human well-being will be far, far greater than

any benefits. We can be certain of this

because the human presence in the world

is so enormous and the infrastructure we

require to sustain our fantastically complex

economic arrangements is so vulnerable to instability. That ought to be the meaning of the Russian heat wave and other extreme climate events. They are the consequence of less than 1℃ of warming; there’s much more to come, and we haven’t begun to seriously address the problem.

Here’s a short list of some of the certain consequences of a warmer world

           Heavier rain & more floods

           Dry places (specially in the sub-tropics) will get much drier

           A lot of agricultural land will be lost, affecting food production

           Storms (specially tropical storms) will be more severe

           Heat waves will be more common, severe and dangerous

           Wildfires will be much worse

           The sea will rise, probably for centuries, with a final level possibly tens of metres higher

           The oceans will warm and acidify, causing very big losses of marine life

           Many species won’t adapt to the rapid warming and will succumb

           There are some geophysical consequences which will act as strong positive feed-backs, amplifying the warming. Nobody knows in detail what it would take to trigger them (although there are ominous signs already) but there’s potential for the warming to become unstoppable should they really get going.

A skeptical footnote

In science every claim is assessed on the evidence provided for it. Scientists are supposed to regard ALL evidence impartially, and to be good at judging which part of the evidence counts most for or against any proposition. Science is conducted as an open conversation, so that anyone can check for themselves whether a conclusion is justified. In science, having an open mind means being prepared to go where the evidence leads.

Anyone who begins with a belief, then looks for evidence to support it, ignoring the rest, is not doing science. This is the way propagandists and preachers work. It is about as unscientific as you can get.

If you investigate the problem of climate change at all, you’ll encounter many claims that seem to contradict it - for example, that warming stopped in 1998; or that warming is due to the sun; or CO₂ is harmless; or the temperature record is false; or that the severity of the problem has been exaggerated by “alarmists”, including climate scientists. I have provided answers to many of these on this site, but if you want to get detailed answers to all of them, you should use the superb site www.skepticalscience.com, which is devoted to this. I’ve given links to a number of others on the links page here.

Are scientists in serious disagreement about the climate problem?

You could easily get the impression that the scientific community is deeply divided over climate change – and indeed there are quite a few scientists who publicly and often deny that it is a problem. But it’s important to know that almost none of these is a practicing climate specialist, and many (not all) have links with either the fossil fuel industry or right-wing political institutes. By itself, that does not mean that they can’t be right – on the other hand, since this is an expert matter, dissent would count much more if it came from amongst those experts. So how much do they disagree?

Naomi Oreskes, History of Science Professor at the University of California, San Diego, did a study in 2004 to answer this question. [Use the link to read it] By examining a sample of nearly 1000 peer-reviewed papers published in the major journals between 1993 & 2003 she showed that no working scientist – not one – could be found who disputed the basic propositions of anthropogenic (man-made) climate change.

Among the people in the best position to know and understand, there is no disagreement whatsoever.

So where’s the argument coming from? It turns out that it is a fairly recent thing. It started after the US delegation signed the Earth Summit Treaty in Rio in 1992, while that country was deliberating its commitment to the Kyoto protocol. It is highly political and emotive, rather than scientific, and the arguments used to oppose climate change action are easily answered and have been refuted over & over by concerned and patient scientists. Yet they continue. You shouldn’t be surprised to know that Oreskes’ study too has been attacked by the same people. She and Erik Conway have since written an excellent book about the origins of the climate denial movement [Merchants of Doubt. 2010; Bloomsbury].

John Cook has done an exhaustive update and confirmation of Oreskes study, which you can find here.

Several recent studies have shown how very unusual these severe heat waves are, and how they will become much more common in future.

See, for example,

Nobody has ever lived in a warmer world, so how can we be sure what it will be like?

Predicting the consequences of a sustained energy imbalance is, indeed, the biggest research challenge of our times.

Scientists working on these difficult and urgent questions have three sources of new knowledge:

•  Careful observations of the trends taking shape around us - eg glacier melting; frequency of droughts, floods, severe storms and heat-waves; effects on the biosphere; impacts on the complex social world, and many more.

•  Study of Earth's climate history - the best insight into how the climate system behaves under changing conditions.

•  Experiments performed on very sophisticated climate models. These are used to answer questions derived from observations. For example, if it is known what the temperature and sea-level were at some past era, you might want to know which parts of the polar ice caps survived, and why. Or you might want to simulate the effects of chronically reduced rainfall in the Amazon basin, or the likely behaviour of malarial mosquitos when the subtropical zones expand, as they are expected to do.

The enormous effort expended on this kind of research in many disciplines is paying off, as we get more confidence in the predictions, and major discoveries are published all the time. This is probably the largest intellectual enterprise in the world today, and the most productive - simply because it is so important.

Don't let anyone tell you we don't have a clue. Scientists are the first people to acknowledge we don't yet know all the answers ... the fact is we know more than enough to go into bat for the people of the future.

Some people say this isn't much of a problem because it's no different to episodes of past natural climate change.

They are wrong.

When was the last time CO2 was 400 ppm (where it will be in 2016)?

About 3 million years ago.

When was the last time CO2 was sustained between 400 & 425 ppm (where it will be during the 2020s)?

About 15 million years ago.

What was the world like then?

That era (the middle Miocene) was about 3℃ warmer than now; the sea was 25-40 metres higher; there was no ice in the northern hemisphere.

When was the last time CO2 increased as fast as it is now?

Nothing comparable has been found in the climate record. As far as we can tell, the present rapid rise is unique.

The climate problem is often misrepresented. It isn't really about the air getting a couple of degrees warmer ...

it's about solar energy that can't escape, and all the consequences of adding energy to the surface of the Earth.