Climate change: Hiatus-shmiatus, or cold reality?

The so-called hiatus, or pause, in global warming has been a hot topic (yes, pun intended) in the climate science field in recent years.

Of course, the public conversation around this topic has become a magnet for extremist views and denialists shouting “I told you so!” Equally, however, this climate conundrum has spurred widespread research into just what has caused the slow-down in warming and why sophisticated climate models didn’t see it coming.

So, what do we make of all this?

The data

First up, let’s look at this freely available (thanks NOAA) graph. It shows global average temperatures for the last 100 years as anomalies from the average temperature for the whole 20th century.

AGW graph NOAA

Global temperature 1914-2013. From www.ncdc.noaa.gov/cag/time-series/global

It doesn’t take much scientific training to see the overall positive trend represented by that black line.

Zooming in a little, we can also see that since 1914, there have been periods in which annual temperatures increased rapidly, and periods in which they remained static or decreased. This graph speaks to the fact that the climate system is naturally variable on all time scales – from minutes (see Melbourne’s crazy weather!) to decades, centuries and longer.

The 15 years from 1998-present fits the ‘static temperatures’ category. 1998 was the hottest year on record at the time, featuring a strong El Nino and plenty of damaging extreme weather events. Since then, we can see above that warming has not continued at the rapid pace of the 1980s and 1990s.

Denial tactics

Around 2009, the climate denial community began to use this 1998-present period as a flimsy argument that global warming had stopped. This line of inquisition quickly gathered steam as prestigious outlets such as Fox News took up the attack. But wait – 2005 and 2010 are warmer than 1998! Oh, well it must be a pause in global warming then. The angle changed, but the basic problem remained – there are at least 83 ways to manipulate the data to suit your argument.

Barney

Image by Werner Reischel from Flickr [CC BY 2.0]

Picking the very warm 1998 as the starting point for this famous pause in global warming does indeed reveal a relatively flat or negative temperature trend, depending on the end point. But if I were to randomly pick 1995 as the start point, suddenly the warming trends look about twice as strong. Making statements based on short time frames is not an accurate way of talking about the climate system – we can find trends everywhere.

Skeptical science escalator

Temperature trends are everywhere. From www.skepticalscience.com

Still, it is quite plain that the rate of warming has slowed in the last decade or so, despite greenhouse gases reaching increasingly high levels. What is more, continued media attention forced the IPCC to acknowledge that “models do not generally reproduce the observed reduction in surface warming trend over the last 10-15 years.” Undaunted by such concepts as logic and reason, climate change deniers such as Andrew Bolt (don’t waste your time reading this article) continue to jump to ludicrous conclusions based on scientists doing what they do – not jumping to conclusions.

What caused the pause?

Plenty of research has come out in the last few years attempting to pin down the cause(s) of the slowdown in global warming. Several causes have been proposed:

  • More heat being stored in the ocean. Trade winds in the equatorial Pacific have been anomalously strong over the past 15 years, causing warm surface waters to mix more with deeper, cooler waters.
  • Increased volcanic activity. Volcanoes spew out particles which lower the amount of sunlight getting through the atmosphere
  • More aerosols and pollutants in the atmosphere
  • Fluctuations in solar activity

The bottom line is, we don’t really know. The storing of excess heat in the ocean is the most likely culprit, but the atmosphere is a complicated, chaotic system by nature which we will never totally understand.

But nit-picking over such issues as the global warming hiatus is just petty. We know enough to realise that we are playing Russian roulette with our climate system, and the gun is well and truly loaded. Eventually we will feel the consequences of it – hiatus or not.

Further reading:

Trenberth, K. 2013 An apparent hiatus in global warming?

The Guardian: The ‘pause’ in global warming is not even a thing


9 Responses to “Climate change: Hiatus-shmiatus, or cold reality?”

  1. dcrock says:

    Wise words, Abraham.

  2. asjones says:

    As i was reading this blog post, i couldn’t help but think of a couple of quotes i’d previously read on the topic of statistics:

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” – Aaron Levenstein

    “Statistics are like prisoners under torture: with proper tweaking you can get them to get them to confess to anything” – John Rotchchild

  3. dcrock says:

    @mlakidang – I wasn’t talking about geoengineering, no.

    Basically, more pollution and smog in the atmosphere can have a slight cooling effect by not letting as much sunlight/radiation through the atmosphere.

    This effect is seen most notably after large volcanic eruptions i.e. Mt Pinatubo in 1991 – temperatures were lower for 3-4 years after that as it released so much ash, sulfur and aerosol material into the atmosphere.

    Aerosols and pollution can also have a cooling influence (very slight though) in Asian countries where the air quality is often terrible.

  4. mlakidang says:

    Interesting. You’ve mentioned about the causes of pause “…More aerosols and pollutants in the atmosphere”. Is this related to geoengineering experiment? Thanks

  5. dcrock says:

    Thanks guys!

    Toni – there is always variability in the climate system as it is a dynamic, chaotic system. But the recent warming is well outside the bounds of expected natural variability.

    Peter – that site is hilarious, I have seen it previously! It also reminds me of the Flying Spaghetti Monster bible where they correlate number of pirates worldwide with belief in the FSM (I think).

    Sarah – yeah sorry, there was a scale on the right in Fahrenheit but I removed it. The anomalies for the last 10-15 years are all in the +0.5-0.6 C range… The scale is in 1C increments so it doesn’t show up well unfortunately.

  6. Sarah Webber says:

    Great post – I love your break down of some of the dodgy ways numbers are used in this debate! Do you know, for the NOAA graph, what is the vertical scale? It’s weird that it’s not shown on the graph.

  7. Peter Ge says:

    Oh my god that graph has just opened up my eyes to how easily data can be distorted. Have you seen this site? http://tylervigen.com/
    It has a lot of funny examples of statistical correlations that don’t actually mean anything.

  8. griffith says:

    This was a great piece!

    It really highlights how easily data and statistics can be manipulated to support ones own theory – eye opening especially for us scientists competing with the likes of news media outlets. The use of that graph comparing skeptics vs. realists was perfect to truly visual make your point.

    It really reminded me of the ‘documentary’ The Great Global Warming Swindle – an interesting piece on scientists who state that Global Warming is just a normal process of the environment!

  9. tonih says:

    Interesting post. I know that a lot of climate deniers mix up the weather with overall climate trends. Surely if there are anomalies in global average temperatures then that is a sign of the increasingly fluctuating and unstable state of our climate?