Global Warming Basics: What It’s NOT


In every province, the chief occupations, in order of importance, are lovemaking, malicious gossip, and talking nonsense.
— Voltaire, Candide

Whether we refer to the subject as “climate change” or “global warming,” it’s a good idea to know what it is we’re talking about. Yet true to Voltaire’s form, we indulge in a great deal of talking nonsense about it. Therefore let me say a few things about what it is not.


Global warming is NOT the end of weather

In February 2015, senator James Inhofe (R-OK) brought a snowball onto the floor of the U.S. Senate. He talked about how cold it was outside, calling the temperature “unseasonable,” and cavalierly tossed the snowball to the senate president with the words “catch this.” It was his attempt to ridicule those who call global warming a problem.

He succeeded in bringing down ridicule — on himself. That’s because, implicit in senator Inhofe’s criticism is the idea that we can discount global warming because he found some cold weather (in winter). Of course the idea is silly, but it’s surprising how many people think that global warming must spell the end of cold. Everywhere. All the time.

Just because climate changes, it doesn’t mean we won’t still have weather. We will, of all kinds: hot, cold, wet, dry, windy, calm. The days will continue to bring a never-ending variety of temperatures, from bitter cold to oppressive heat, because nothing will stop them fluctuating from day to day. But if you track temperature every day, you’ll find that the hots are a little hotter and a little more frequent, the colds not quite so cold nor quite so common.

Global warming is NOT the fluctuations — it’s the trend

One of the most common misconceptions is that if global warming is really happening, each year must be hotter than the one before.

Temperature (and other weather variables) fluctuate, always have, always will. Global warming doesn’t change that (although it might change the essential nature of the fluctuations). What counts is the trend. We’ll still have colder days and hotter days, colder and hotter months, years. But the average, what we expect to happen over long periods of time, is changing persistently.

Global warming is NOT a “little” change

Some make hay of the fact that the average temperature change over the whole globe caused by mankind so far, has only been about 1C (one degree Celsius, equal to 1.8 degrees Fahrenheit). How can that matter, they ask, when temperature may change by 30 degrees or more within a single day? If you raise the temperature of the room you’re sitting in by a “mere” 1C, you might not even notice.

It’s no surprise if a single day is one degree hotter, or even ten. But if temperature is persistently just a little bit hotter on average, the extra heat adds up day in and day out, and the effect can be profound.

Tens of thousands of years ago global average temperature was “only” about five degrees colder. To many, that hardly seems enough to bring about a cataclysm. But Earth was in the grip of a great glaciation, with miles-thick sheets of ice covering what are now the locations of great cities. So much of the world’s water was frozen that the sea stood 400 feet lower than it does today, uncovering great tracts of land.

We’re witnessing big changes already, from only one degree of change. Bayfield, Wisconsin, is a small town on the shore of Lake Superior, best known for its natural landscape and outdoor activities. Every year the lake freezes over, and locals have kept track of how long it stayed that way for over a century. Back in the 1850s and 1860s it was typically ice-covered for about 118 days, but now that the 2000s are here the lake is typically ice-covered for only 53 days. That much decrease — nine weeks, so today’s typical lake ice season is less than half what it used to be — isn’t “little” by anybody’s definition.

Many other huge changes (“you can’t miss it” as opposed to “you might not even notice”) have taken place, due to the 1C we’ve warmed the planet so far. The consensus of climate scientists is that if we go twice as far, up to 2C, the cost (in lives lost, refugees, crop failures, drought, flood, sea level rise, and more) will be far more than we want to face. Noone knows how bad it will get beyond that, 3C or even more, and nobody in his right mind wants to find out.

Global warming is NOT the same everywhere

Many believe that global warming is uniform, i.e. that every place on Earth will warm at the same rate. But the differences between regions have caused them to warm by different amounts.

The oceans have huge “thermal inertia,” so it takes more heat to warm them than it does the land. Since the northern hemisphere has so much more land than the southern (most of the world’s land is in the northern half of the globe), it has warmed considerably faster. The Arctic is warming most quickly, about 3 1/2 times as fast as the globe as a whole.

This figure (from NASA) shows how much different parts of
the world have warmed, by comparing the 2005-2015 average to the 1951-1980 average.

NASAmap

Global warming is NOT the same at all times

We’ve already emphasized that temperature is always fluctuating as heat moves from land to air to sea; even when averaged over an entire year, fluctuation persists. But it’s also important to realize that the trend hasn’t been the same at all times either.

As figure this graph shows, not only has there been a pattern to the world’s temperature changes, there are year-to-year fluctuations which can make one year cooler than the previous, even in a warming world:

GISStemp

It also reveals unsteadiness of the trend itself; the early 20th century saw a period of warming which was followed by several decades of none. Since about 1970, however, the trend has been steadily upward. The overall pattern is found not only in the temperature at Earth’s surface (where we live), but in the depths of the oceans as well.

Global warming does NOT cause all extreme weather — but it causes more

Lately, whenever extreme weather brings disaster someplace, two reactions are common. Some will talk about how this may be directly related to climate change. Others will retort that extreme weather has been happening always, and you can’t prove this particular event was caused by anything unnatural.

It’s true that you can’t prove any single event was caused by global warming. It’s also true you can’t prove any home run in a baseball game was “caused by” steroids. Major leaguers have been hitting home runs as long as we’ve played baseball — but when steroid use became endemic, the number of home runs went up. By a lot — enough that we could tell, steroid use might not have “caused” any particular home run, but it was causing more than we got without.

Climate change has been likened to “weather on steroids.” We can’t blame it for that particular heat wave, but we can definitely blame it for the increase. And, like steroids, it doesn’t just cause extreme events to be more common, it make them more extreme.

Global warming did NOT recently “pause”

Even when the trend is steadily upward, fluctuations can make it seem otherwise. That’s the nature of fluctuations; by going down they can mask a trend in the opposite direction.

One of the most persistent, and most effective, talking points of those who deny the reality of global warming is that temperature increase recently showed a “pause” or “hiatus.” Such claims usually start with the year 1998 because that was when the fluctuation was exceptionally high, so much so that it took years for the upward trend to overtake it. A favorite trick is to show a graph of global temperature like this:

pause

It shows the period of the so-called “pause” but not what came before. Including context would cast doubt on the “pause” claim, and might even reveal that short periods of time — less than about 30 years — aren’t enough to reveal the genuine climate trend, they’re dominated by weather fluctuations.

Some context is necessary, like this:

nopause

It makes plain the lack of support for the “pause” idea. Not only does what came before show this, what has happened after 2013 makes the idea look rather silly. Since 2014 was a new record hottest year, and 2015 broke the record again, talk of the “pause” has shifted to other strategies, including casting doubt on the data itself, and pointing to different data as though it were better when in fact it’s not.

When someone shows a graph which doesn’t start until 1997 or 1998, refusing to show what came before, ask yourself why they’re not telling the whole story.


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24 responses to “Global Warming Basics: What It’s NOT

  1. “Climate change has been likened to ‘weather on steroids.’ We can’t blame it for that particular heat wave, but we can definitely blame it for the increase.”

    I wish scientists would be clearer about which definition of climate change they are using in a given case.

    The “narrow” definition: a change in climate, i.e., a change in the statistics of weather.

    The “broad” definition: a change in the climate system, i.e., a change in the global physical, chemical, biological system that produces weather.

    We might say that climate change in the narrow sense is a “trailing” indicator reflecting the fact that something has happened; it doesn’t “cause” or “affect” anything. On the other hand, climate change in the broad sense is a “leading” indicator and suggests what kind of weather will happen; it “affects” all the weather.

    • A nicely drawn distinction. Maybe we should use the term “Earth System change” for what you term the ‘broad definition.’

      • Actually, it’s not “my” distinction. I picked it up from the 4th IPCC report back when. I quote:

        “Climate change refers to any change in climate over time, whether due to natural variability or as a result of human activity.”

        So what is “climate”? Again, I quote:

        “Climate in a narrow sense is usually defined as the ‘average weather’, or more rigorously, as the statistical description interms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.”

        “The climate system is defined by the dynamics and interactions of five major components: atmosphere, hydrosphere, cryosphere, land surface, and biosphere. Climate system dynamics are driven by both internal and external forcing, such as volcanic eruptions, solar variations, or human-induced modifications to the planetary radiative balance, for instance via anthropogenic emissions of greenhouse gases and/or land-use changes.”

        Taken from https://www.ipcc.ch/publications_and_data/ar4/wg2/en/annexessglossary-a-d.html

      • Ah! The honest man refusing credit from the less-informed!

        :-)

  2. If something happens that is unprecidented can that be attributed to AGW? Hurricane Sandy was a month after any previous hurricane had been observed in that area. The recent South Carolina floods were much higher than previous records. What is needed to be able to say “this one was caused by AGW”?

    Some changes, like sea level rise, can be attributed solely to AGW.

    • It’s a matter of probabilities; certain events like exceptionally strong storms or storms outside of a normal season are *more likely* because of AGW, but that doesn’t mean any one specific weather event is definitely caused by AGW, and there’s really no way AFAIK to make such a determination. Sometimes weather is just weather, independent of any change in climate.

      Changes in weather *patterns* (number and intensity of storms) can be attributed to AGW pretty clearly. though.

      • The North Pacific area of hotter surface water and the colder area of surface water in North Atlantic would be contenders of weather phenomena attributable solely to agw, though. At least I’ve not heard of any such happening since the end of last glacial.

    • Not quite. Groundwater depletion also contributes. And yes, that’s anthropogenic, too, but still…

    • In the case of hurricanes, I would say that the historic record is not long enough to say with a high degree confidence that any particular event is unprecedented. It may not have a precedent in the historic record, but that does mean it has not occurred previously under the current climate system, which is many centuries longer than any North American historical records.

  3. In any complex system “causation” is a really difficult subject. There are ways to get at what you’re talking about, but it will never result in “A caused B”.

    For some approaches think path analysis (http://crab.rutgers.edu/~goertzel/pathanal.htm) or at least simple mediator variable analysis ((http://davidakenny.net/cm/mediate.htm).

  4. I suggest supplementing your last graph with the corresponding graph that you and Stefan Rahmstorf published with the natural climate variation removed, or showing an update thereof.

  5. ” …but that doesn’t mean any one specific weather event is definitely caused by AGW…”

    I find this to be the deliberately wrong question to ask, considering that we now live on a planet that has accumulated much more heat in air, land, and water and 5% more water vapor than were present in the 19th century.

    I think it would be much more proper to say that it would not be possible to say that any one specific weather event was NOT caused by AGW in 2016. For example, the atmospheric conditions which produced a beautiful 70F day in the U.S. in June of 1850 are not the same as would produce an exactly similar day on 2016 – because of all the extra energy in the system today.

    In other words, weather is NOT weather when you have two different climate systems.

  6. As the readers of this blog and of Tamino know, rational debate only works on the rational … and we are a few short of that mark with some of those active in this area …

    “As the scientific consensus for climate change has strengthened over the past decade, the arguments against the science of climate change have been on the increase.”

    “That’s the surprise finding of a study, published in the journal Global Environmental Change last month, which analysed and identified the key themes in more than 16,000 publications about climate change by conservative organisations.”

    https://theconversation.com/the-science-for-climate-change-only-feeds-the-denial-how-do-you-beat-that-52813

  7. Errata: oops in my last comment
    that was a NASA graph I was referring to. Titled “no significant change in trend sine 1998.”

  8. “Global warming does NOT cause all extreme weather — but it causes more

    Lately, whenever extreme weather brings disaster someplace, two reactions are common. Some will talk about how this may be directly related to climate change. Others will retort that extreme weather has been happening always, and you can’t prove this particular event was caused by anything unnatural.

    It’s true that you can’t prove any single event was caused by global warming. It’s also true you can’t prove any home run in a baseball game was “caused by” steroids. Major leaguers have been hitting home runs as long as we’ve played baseball — but when steroid use became endemic, the number of home runs went up. By a lot — enough that we could tell, steroid use might not have “caused” any particular home run, but it was causing more than we got without.

    Climate change has been likened to “weather on steroids.” We can’t blame it for that particular heat wave, but we can definitely blame it for the increase. And, like steroids, it doesn’t just cause extreme events to be more common, it make them more extreme.”

    I only recently started researching climate change for a physics project, so I found your description of global warming’s role in extreme weather to be very helpful. Too often, I believe that the “average person” misinterprets global warming as an unusual “heat wave” in the middle of December (as we had this year in southern PA). Your post explains very clearly that the concept of global warming is more related to the overall trends that have occurred over time. One of the article’s that I read when beginning my research described the point that many people think that a colder than average winter in one area means that temperatures are colder than average on a global scale, as your blog acknowledges, this is certainly not the case.

  9. Methane madness

    In Australia the fire season has expanded so that it now coincides with a large
    amount of un-reaped crops. This had devastating repercussions in dec.2015, South
    Australia, with a deadly fire. This fire could not be called a bush fire, as there is little ‘bush’ on crop land, it is a new phenomenon: crop fire.

    On the ‘missing heat’ issue, my Physics Proffesor said that increased energy in the system will increase Kinetic energy of planet increasing Planets angular velocity.

    [Response: I don’t see how increased kinetic energy (from increased heat) will increase angular velocity. The angular *momentum* is conserved except for influences which exert a torque (the moon does that through the tides, but the effect is small), and the only way to alter angular velocity without altering angular momentum is to change the planet’s moment of inertia about its rotation axis. Ask your physics professor how that happens?]

    • Global warming is resulting in a slowing of the earth’s rate of rotation (slightly lengthening the day). Solid water in polar ice sheets (close to the axis of rotation) is converted to liquid water, some of which moves toward the equator (farther from the axis of rotation). This redistribution of mass requires a slower rotation to conserve the angular momentum. It is like a spinning figure skater extending arms out from the body to slow the spin. The effect is very small but measurable. For example, see http://advances.sciencemag.org/content/1/11/e1500679

  10. Methane Madness,
    I agree with Tamino. This doesn’t make sense the way you’ve phrased it. There is an effect on angular rotation, though, as polar ice melts and angular momentum drives it toward the equator. This changes the moment of inertia and SLOWS Earth’s rotation (while not changing its angular momentum as Tamino noted.)

  11. Pete Dunkelberg

    Crop fires? Methane madness, this is interesting. Are others using this term? can you link any articles? Has it happened before? Are there any reliable numbers – acres or dollars or bushels lost?

    Global warming: It is good indeed that you start with physics; that is where it starts, and continues on while spreading into chemistry, biology and human life. But once you start learning how things really work, you will forget the idea that you posted.

    Try this. Ask yourself the question “How does a planet get its temperature?”
    Earth, like any planet, is sitting out in space where it is very cold. Down here on the solid & liquid surface we are much warmer than space. Why? And how is the average surface temperature arrived at?

    This may lead you to think about total energy arriving at our surface, and the same amount escaping to space every day. The daily energy in and out must be virtually the same every day, but how does energy get back into space? Give it some thought.

    Meanwhile, can you tell us more about those fires?

  12. Methane Madness

    Never fear Pete Dunkelberg, I’ve been thinking about the Greenhouse effect since about 2006 and gained a level of understanding that enabled me to have a few beers with the chief Climatologist of the Bureau of Met, Adelaide, SA. I said to him “At least we will have a good understanding of how we f*cked up” and he said yes. I was happy with my understanding of climate science and have now moved into Nuclear Physics.
    The fire is known as the Pinery fire (Australia) and resulted in destruction of 15 million in un-harvested grain and burnt out 217000 acres overall http://pir.sa.gov.au/alerts_news_events/news/primary_industries/cropping_losses_from_pinery_fire_estimated_at_24m
    This has only happened once, on a smaller scale, before.
    No one is calling it a crop fire, only me, for want of a accurate name, as it cannot be called a bush fire, as there is no ‘bush’ in the area, it is all cleared for cropping. The key point is that fire season used to fall during the period when there was only stubble in the fields, after they had been harvested, now it falls prior significant harvest of wheat, of course leading to the possibility that this is just the start.
    This fire was very fast, my family lives in the area and they said it travelled about 40 kilometers in 3 hours, which suggests just how volatile crops are, but it makes sense as they are very dry and have low mass so don’t take long to warm up to ignition point.
    http://www.adelaidenow.com.au/news/south-australia/pinery-fire-dramatic-video-by-british-tourists-shows-devastating-speed-and-size-of-fire/news-story/72c1648483dba1042cb676500e2612c5
    I note that the tourist said no one warned them of such a possibility.. because its never happened before.

    As for how my professor explains increased speed of Earth due to increased energy, I’ll go out on a limb and say he’s using relativistic principles. We are on break at the moment so I won’t hold my breath for his reply.

  13. Pete Dunkelberg

    Thanks for the explanation.

  14. Methane madness

    The Professor has no recollection of a statement regarding Earths angular velocity and goes on to explain it is not possible as Tamino does.