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Thoughts on 2014 and ongoing temperature trends

Filed under: — gavin @ 22 January 2015

Last Friday, NASA GISS and NOAA NCDC had a press conference and jointly announced the end-of-year analysis for the 2014 global surface temperature anomaly which, in both analyses, came out top. As you may have noticed, this got much more press attention than their joint announcement in 2013 (which wasn’t a record year).

In press briefings and interviews I contributed to, I mostly focused on two issues – that 2014 was indeed the warmest year in those records (though by a small amount), and the continuing long-term trends in temperature which, since they are predominantly driven by increases in greenhouse gases, are going to continue and hence produce (on a fairly regular basis) continuing record years. Response to these points has been mainly straightforward, which is good (if sometimes a little surprising), but there have been some interesting issues raised as well…
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A new sea level curve

Filed under: — stefan @ 14 January 2015

The “zoo” of global sea level curves calculated from tide gauge data has grown – tomorrow a new reconstruction of our US colleagues around Carling Hay from Harvard University will appear in Nature (Hay et al. 2015). That is a good opportunity for an overview over the available data curves. The differences are really in the details, the “big picture” of sea-level rise does not change. In all curves, the current rates of rise are the highest since records began.

The following graph shows the new sea level curve as compared to six known ones.

haysl1

Fig 1 Sea level curves calculated by different research groups with various methods. The curves show the sea level relative to the satellite era (since 1992). Graph: Klaus Bittermann.

All curves show the well-known modern sea level rise, but the exact extent and time evolution of the rise differ somewhat. Up to about 1970, the new reconstruction of Hay et al. runs at the top of the existing uncertainty range. For the period from 1880 AD, however, it shows the same total increase as the current favorites by Church & White. Starting from 1900 AD it is about 25 mm less. This difference is at the margins of significance: the uncertainty ranges overlap. More »

References

  1. C.C. Hay, E. Morrow, R.E. Kopp, and J.X. Mitrovica, "Probabilistic reanalysis of twentieth-century sea-level rise", Nature, 2015. http://dx.doi.org/10.1038/nature14093

Absolute temperatures and relative anomalies

Filed under: — gavin @ 23 December 2014

Most of the images showing the transient changes in global mean temperatures (GMT) over the 20th Century and projections out to the 21st C, show temperature anomalies. An anomaly is the change in temperature relative to a baseline which usually the pre-industrial period, or a more recent climatology (1951-1980, or 1980-1999 etc.). With very few exceptions the changes are almost never shown in terms of absolute temperatures. So why is that?

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The most popular deceptive climate graph

The “World Climate Widget” from Tony Watts’ blog is probably the most popular deceptive image among climate “skeptics”.  We’ll take it under the microscope and show what it would look like when done properly.

So called “climate skeptics” deploy an arsenal of misleading graphics, with which the human influence on the climate can be down played (here are two other  examples deconstructed at Realclimate).  The image below is especially widespread.  It is displayed on many “climate skeptic” websites and is regularly updated.

Watts_world_climate_widget

The “World Climate Widget” of US “climate skeptic” Anthony Watts with our explanations added.  The original can be found on Watts’ blog

What would a more honest display of temperature, CO2 and sunspots look like? More »

Recent global warming trends: significant or paused or what?

As the World Meteorological Organisation WMO has just announced that “The year 2014 is on track to be the warmest, or one of the warmest years on record”, it is timely to have a look at recent global temperature changes.

I’m going to use Kevin Cowtan’s nice interactive temperature plotting and trend calculation tool to provide some illustrations. I will be using the HadCRUT4 hybrid data, which have the most sophisticated method to fill data gaps in the Arctic with the help of satellites, but the same basic points can be illustrated with other data just as well.

Let’s start by looking at the full record, which starts in 1979 since the satellites come online there (and it’s not long after global warming really took off).

trend1Fig. 1. Global temperature 1979 to present – monthly values (crosses), 12-months running mean (red line) and linear trend line with uncertainty (blue) More »


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