The Greenhouse Effect is Real – Here’s why

June 15, 2011

In an “Open letter from the Scientific Community”,  a series has begun this week in The Conversation,  (a not-for-profit news service  backed by CSIRO – Australia’s leading science organization – and Australia’s leading universities)  –  “Climate Change is Real: An Open Letter from the Scientific Community“.

Part 2, just published, is headlined The Greenhouse Effect is real – Here’s why.
I’m pairing it with the above video on “What Do We Know about Climate Change?” – both answer basic questions for the newcomer on what scientists know about climate, and why we have a problem.  The “Conversation” piece, written by Bureau of Meteorology scientist Karl Braganza, discusses fundamental issues in clear english – reprinted below —

In public discussions of climate change, the full range and weight of evidence underpinning the current science can be difficult to find.

A good example of this is the role of observations of the climate system over the past one hundred years or more.

In the current public discourse, the focus has been mostly on changes in global mean temperature.

The greenhouse effect is fundamental science

It would be easy to form the opinion that everything we know about climate change is based upon the observed rise in global temperatures and observed increase in carbon dioxide emissions since the industrial revolution.

In other words, one could have the mistaken impression that the entirety of climate science is based upon a single correlation study.

In reality, the correlation between global mean temperature and carbon dioxide over the 20th century forms an important, but very small part of the evidence for a human role in climate change.

Our assessment of the future risk from the continued build up of greenhouse gases in the atmosphere is even less informed by 20th century changes in global mean temperature.

For example, our understanding of the greenhouse effect – the link between greenhouse gas concentrations and global surface air temperature – is based primarily on our fundamental understanding of mathematics, physics, astronomy and chemistry.

Much of this science is textbook material that is at least a century old and does not rely on the recent climate record.

For example, it is a scientific fact that Venus, the planet most similar to Earth in our solar system, experiences surface temperatures of nearly 500 degrees Celsius due to its atmosphere being heavily laden with greenhouse gases.

Back on Earth, that fundamental understanding of the physics of radiation, combined with our understanding of climate change from the geological record, clearly demonstrates that increasing greenhouse gas concentrations will inevitably drive global warming.

Dusting for climate fingerprints

The observations we have taken since the start of 20th century have confirmed our fundamental understanding of the climate system.

While the climate system is very complex, observations have shown that our formulation of the physics of the atmosphere and oceans is largely correct, and ever improving.

Most importantly, the observations have confirmed that human activities, in particular a 40% increase in atmospheric carbon dioxide concentrations since the late 19th century, have had a discernible and significant impact on the climate system already.

In the field known as detection and attribution of climate change, scientists use indicators known as fingerprints of climate change.

These fingerprints show the entire climate system has changed in ways that are consistent with increasing greenhouse gases and an enhanced greenhouse effect. They also show that recent, long term changes are inconsistent with a range of natural causes.

Is it getting hot in here?

A warming world is obviously the most profound piece of evidence.

Here in Australia, the decade ending in 2010 has easily been the warmest since record keeping began, and continues a trend of each decade being warmer than the previous, that extends back 70 years.

Globally, significant warming and other changes have been observed across a range of different indicators and through a number of different recording instruments, and a consistent picture has now emerged.

Scientists have observed increases in continental temperatures and increases in the temperature of the lower atmosphere.

In the oceans, we have seen increases in sea-surface temperatures as well as increases in deep-ocean heat content. That increased heat has expanded the volume of the oceans and has been recorded as a rise in sea-level.

Scientists have also observed decreases in sea-ice, a general retreat of glaciers and decreases in snow cover. Changes in atmospheric pressure and rainfall have also occurred in patterns that we would expect due to increased greenhouse gases.

There is also emerging evidence that some, though not all, types of extreme weather have become more frequent around the planet. These changes are again consistent with our expectations for increasing atmospheric carbon dioxide.

Patterns of temperature change that are uniquely associated with the enhanced greenhouse effect, and which have been observed in the real world include:

  • greater warming in polar regions than tropical regions
  • greater warming over the continents than the oceans
  • greater warming of night time temperatures than daytime temperatures
  • greater warming in winter compared with summer
  • a pattern of cooling in the high atmosphere (stratosphere) with simultaneous warming in the lower atmosphere (tropopause).

How do we know it’s us?

By way of brief explanation, if the warming over the 20th century were due to some deep ocean process, we would not expect to see continents warming more rapidly than the oceans, or the oceans warming from the top down.

For increases in solar radiation, we would expect to see warming of the stratosphere rather than the observed cooling trend.

Similarly, greater global warming at night and during winter is more typical of increased greenhouse gases, rather than an increase in solar radiation.

There is a range of other observations that show the enhanced greenhouse effect is real.

The additional carbon dioxide in the atmosphere has been identified through its isotopic signature as being fossil fuel in origin.

The increased carbon dioxide absorbed by the oceans is being recorded as a measured decrease in ocean alkalinity.

Satellite measurements of outgoing long-wave radiation from the planet reveal increased absorption of energy in the spectral bands corresponding to carbon dioxide, exactly as expected from fundamental physics.

It is important to remember that the enhanced greenhouse effect is not the only factor acting on the climate system.

In the short term, the influence of greenhouse gases can be obscured by other competing forces.

These include other anthropogenic factors such as increased industrial aerosols and ozone depletion, as well as natural changes in solar radiation and volcanic aerosols, and the cycle of El Niño and La Niña events.

By choosing a range of indicators, by averaging over decades rather than years, and by looking at the pattern of change through the entire climate system, scientists are able to clearly discern the fingerprint of human-induced change.

Case closed

The climate of Earth is now a closely monitored thing; from instruments in space, in the deep ocean, in the atmosphere and across the surface of both land and sea.

It’s now practically certain that increasing greenhouse gases have already warmed the climate system.

That continued rapid increases in greenhouse gases will cause rapid future warming is irrefutable.


12 Responses to “The Greenhouse Effect is Real – Here’s why”

  1. omnologos Says:

    Braganza forgot to say how much the “irrefutable” “rapid future warming” is expected to be? I suspect that from a public-policy point of view, that details makes all the difference.

    Also the mention of “rapid” in “continued rapid increases” and “future warming” is ambiguous. It almost sounds as if the issue is the speed of increase in GHGs rather than the increase in GHGs itself?

  2. rpauli Says:

    The real phenomenon is the power of idiotic cretins to perpetuate this anti-science, pro-risk carbon indulgence long past the time when we first knew – in the early 1970s – and into the 1980s – when we started to understand the greenhouse mechanism. A concept as easy to understand as boiling water.

    Mitigation is now impossible, long live adaptation.

    All major nation’s military forces know the science and are seriously preparing.

    And now we are left again to be plundered by the insurance industry – which has long accepted global warming – after all their business is actuarial risk.

    The tactic of skeptical distraction has succeeded. Peter, you and I are left squabbling with babbling, mumbling ideologues – fighting over just what place in line we will all hold… but those who are still debating are only slightly ahead of the authentic denialists.

    As Oreskes says – For the last 150 years we have been at a grand and gluttonous carbon feast, – and now the waiter is presenting the bill. The consequences of continued risk are ruthlessly well known. Now we are now in the climate drama called Waiting for Godzilla.

    • omnologos Says:

      Mitigation is now impossible, long live adaptation

      I agree. I don’t think Peter Sinclair does. I’m also afraid adaptation is hampered by the UN inertia, that will see the focus wastefully stuck to “mitigation” for years still if not decades.

      • greenman3610 Says:

        it’s been said our choices are now, mitigation, adaptation, or suffering.
        Those of us who’ve been warning about the suffering are aware that the planet is going to take a hit. The question is, how much of a hit.
        I’d like to keep it something short of mass extinction, and I think mitigation is in order to do that.
        The process will not be a pleasant one for much of the planet – but, like a heart attack victim who changes his ways and finds a better life, we could come out of this a happier place, maybe with most of our ecosystem intact.
        Since I have kids, I prefer to work for that. You may have other priorities.

        • rpauli Says:

          nice analogy – the individual heart attack patient – and civilization.

          But the patient is still in the early phases of a heart attack – and just because he knows he is starting to suffer, does not mean it is over with.

          Mass extinction is a non-zero possibility – and we cannot discount it just because nobody wants it to happen. That is not a fair practice of science.

          All the hockey stick charts stop at the year 2100 only because it is a nice round number — not because it will end there.

          All the warming and destabilization and sea level rise are still modeled to rise and increase – it is just that tipping points make it very unknown and unknowable.

          It is not that we are alarmist, it is that we are not sufficiently alarmed.

          The tone of your videos is perfect, and you do excellent communication – but we all are in varying degrees of denial – it is very tough to ruthlessly assess the situation when in the middle of a heart attack. I consider suffering to be a form of adaptation.

  3. omnologos Says:

    it’s exactly because I have kids that I want to do what is possible instead of dying for yet another false ideology. If you know of any mitigation that’d do better than adaptation, I’m all ears for that. You might want to inform the UK government too as they are clueless on the topic despite being committed to it.

  4. witsendnj Says:

    I don’t think characterizing realism as having “other priorities” is quite fair. I’ve got kids too – they are my priority. I love them more than anything – I want them to not only survive, but live the futures I (mistakenly) brought them up to expect they would inherit – careers in law, veterinary medicine, and teaching biology at the college level. You know, work hard and you will earn a nice life, with a lovely family, living in security, in a beautiful world resplendent with nature’s bounty.

    I now know that is impossible. There is too much heating in the pipeline, the amplifying feedbacks have been set in motion and cannot be reversed, in other words, that “uninhabitable climate” cake has been baked and there is going to be a sudden, terrible breakdown in society and quite likely resource wars.

    You may “prefer” to believe the ecosystem is going to survive intact, but that is simply an impossibility. A rudimentary understanding of evolution precludes any such fantasy, because the eco SYSTEM is an incredibly complex set of relationships that unfolded over time, of different species becoming increasingly dependent on each other for food, shelter, population control, and a million other services to each other – as well as a climate that is stable within certain perimeters, which have already been breached.

    So now my priority with my children (which I confess they do not appreciate in the least) is to help them adjust their expectations and priorities or, failing that (and so far I have failed) to simply last long enough personally in the event that they will need a shoulder to weep on, or perhaps someone to blame, when the full understanding of the catastrophe previous generations have wrought through our selfishness, stupidity, and greed overcomes them.

    • greenman3610 Says:

      good luck with that.

      • rpauli Says:

        There is no more important communication for the future than that we give to our children. Even our adult children.

        And our young adult offspring are the most burdened, because they face colossal change – and they are already shocked by the messages and the reality of the world. [a world increasingly unlike anything we faced as we grew up]

        Messaging to this group will be most difficult – because they must retain their foundation of vision into survival and thriving – while embracing a ruthless assessment of the situation. Failing to apprehend means they quicken the demise. Failure of faith means depressive surrender.

        And we are beginning to see it play out now – more so in the next few dozen years.

        Interesting times.

  5. otter17 Says:

    What’s with this talk of adaptation? From the evidence I have seen so far from Climate Progress (and I believe Peter has mentioned it here), mitigation will likely be cheaper than adaptation and limit the suffering. Now, I agree with Dr. Trenberth in his article “Communicating Climate Science and Thoughts on Climategate” that adaptation ought to be a part of our plans, and I also agree with Bill McKibben’s outlook in “Eaarth” that we need to move towards smaller, more robust regional economies that can withstand the changing climate. Nevertheless, it seems that we have good reason to believe that mitigation through better logistics, better policies, and more renewables deployment can be cheaper and reduce more suffering than adaptation through mega-projects or individuals hunkering down.

    I have heard statements from some scientists that show despair for mitigation possibilities, but there are also those like Dr. Hansen who feel like a carbon tax will provide a good deal of change. I’m putting my vote with the mitigation types. Besides, researchers and engineers have worked hard to create renewable energy solutions. We should at least be able to say we tried to prevent climate change, despite the grim odds.

  6. otter17 Says:

    Anyway, the topic of this post is about this new open letter series written by climate scientists in Australia. From what I have seen so far, they set a good tone. They seem to be straightforward, frank, and concise with their statements and explanations. Good for them. This series should be a level-headed counter to the nutty skeptic types that I hear about down under. We need the same in the USA… badly. We could also use a not-for-profit news service backed by a science organization (like The Conversation).

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