## New IPCC Report (Part 4)

guest post by Steve Easterbrook

(4) Most of the heat is going into the oceans

The oceans have a huge thermal mass compared to the atmosphere and land surface. They act as the planet’s heat storage and transportation system, as the ocean currents redistribute the heat. This is important because if we look at the global surface temperature as an indication of warming, we’re only getting some of the picture. The oceans act as a huge storage heater, and will continue to warm up the lower atmosphere (no matter what changes we make to the atmosphere in the future).

(Box 3.1 Fig 1) Plot of energy accumulation in zettajoules within distinct components of Earth’s climate system relative to 1971 and from 1971–2010 unless otherwise indicated. Ocean warming (heat content change) dominates, with the upper ocean (light blue, above 700 m) contributing more than the deep ocean (dark blue, below 700 m; including below 2000 m estimates starting from 1992). Ice melt (light grey; for glaciers and ice caps, Greenland and Antarctic ice sheet estimates starting from 1992, and Arctic sea ice estimate from 1979–2008); continental (land) warming (orange); and atmospheric warming (purple; estimate starting from 1979) make smaller contributions. Uncertainty in the ocean estimate also dominates the total uncertainty (dot-dashed lines about the error from all five components at 90% confidence intervals).

Note the relationship between this figure (which shows where the heat goes) and the figure from Part 2 that showed change in cumulative energy budget from different sources:

(Box 13.1 fig 1) The Earth’s energy budget from 1970 to 2011. Cumulative energy flux (in zettajoules) into the Earth system from well-mixed and short-lived greenhouse gases, solar forcing, changes in tropospheric aerosol forcing, volcanic forcing and surface albedo, (relative to 1860–1879) are shown by the coloured lines and these are added to give the cumulative energy inflow (black; including black carbon on snow and combined contrails and contrail induced cirrus, not shown separately).

Both graphs show zettajoules accumulating over about the same period (1970-2011). But the graph from Part 1 has a cumulative total just short of 800 zettajoules by the end of the period, while today’s new graph shows the earth storing “only” about 300 zettajoules of this. Where did the remaining energy go? Because the earth’s temperature rose during this period, it also lost increasingly more energy back into space. When greenhouse gases trap heat, the earth’s temperature keeps rising until outgoing energy and incoming energy are in balance again.

You can download all of Climate Change 2013: The Physical Science Basis here. Click below to read any part of this series:

Climate Change 2013: The Physical Science Basis is also available chapter by chapter here:

### 12 Responses to New IPCC Report (Part 4)

1. […] Most of the heat is going into the oceans, causing thermal expansion of the oceans and, hence, sea-level rise, and presenting the possibility that this heat will come back out and contributing to Earth surface warming in addition to the warming which results directly from a warmer atmosphere. […]

2. There’s another thing to note here. As the article and the IPCC indicate, most of the heat is going into the oceans, no doubt. But the amount that goes in, can vary. Matthew England and others have suggested (see http://www.realclimate.org/index.php/archives/2014/02/going-with-the-wind/) that while some of the heat will be permanently stored in the oceans, once “the pump” (predominantly ENSO) stops, some of this heat may return to the surface, contributing energy in addition to that already retained in atmosphere due to radiative forcing and knock-on effects.

3. arch1 says:

I haven’t yet read the others in this series but found article hugely helpful for the layperson – thanks very much!

In the caption labelled “Box 13.1 fig 1″ I’m guessing that “1860-1879″ should be “1960-1979.” Also in the article the reference to the “first graph” having a cumulative total just short of blah blah is a bit confusing since it’s actually the second graph to appear in the present article.

Given our best model of energy loss to space, how good is the agreement between earth’s observed temperature rise and the (highly uncertain) 500 zettajoule difference between the two graphs?

Is the dip in stored energy around year 2000 related to the early-1990s dip in the volcanic aerosols contribution?

What is driving the remarkably linear reductions due to tropospheric aerosols (and can that be expected to continue, as it looks like the one big offset to Well-mixed GHGs)?

• John Baez says:

arch1 wrote:

Also in the article the reference to the “first graph” having a cumulative total just short of blah blah is a bit confusing since it’s actually the second graph to appear in the present article.

That’s my fault—I added the earlier graph to this post because I thought it would help people remember it, but forgot to adjust the wording. I’ve adjusted it now, though it’s still a bit awkward.

I’ll have to let Steve or someone else answer the other questions.

Cumulative energy flux (in zettajoules) into the Earth system from well-mixed and short-lived greenhouse gases, solar forcing,

what means solar forcing here ?

• Nick Barnes says:

“solar forcing” here refers to the *change* in the intensity of solar radiation, or rather the *net change* (incident energy minus reflected energy). The intensity of the sun varies very slightly over time. See http://en.wikipedia.org/wiki/Solar_constant for more information.

“solar forcing” here refers to the *change* in the intensity of solar radiation, or rather the *net change* (incident energy minus reflected energy). The intensity of the sun varies very slightly over time.

Yes but what exactly leads to that energy accumulation?

A regular oscillation of irradiance with a wavelength below the in the diagram indicated time interval can be “seen on average” more or less as a constant radiation and should belong to some kind of equilibrium situation that is in particular I wouldnt suspect that it would contribute to a growth as indicated in the diagram. So I would expect that there must be some longer term trend in the changes of the intensity of solar radiation. But then I don’t know how exactly this diagram was made.

Moreover it seems that there is a trend, however in the wrong direction. That is the regular sunspot activity seems to have been on the decline, which seems to lead to a lower radiation (From chapter 8 page 662)

Satellite observations of total solar irradiance (TSI) changes from 1978 to 2011 show that the most recent solar cycle minimum was lower than the prior two. This very likely led to a small negative RF of –0.04 (–0.08 to 0.00) W m–2 between 1986 and 2008. The best estimate of RF due to TSI changes representative for the 1750 to 2011 period is 0.05 (to 0.10) W m–2. This is substantially smaller than the AR4 estimate due to the addition of the latest solar cycle and inconsistencies in how solar RF has been estimated in earlier IPCC assessments. There is very low confidence concerning future solar forcing estimates, but there is
high confidence that the TSI RF variations will be much smaller than the projected increased forcing due to GHG during the forthcoming decades. {8.4.1, Figures 8.10, 8.11}

So that sounds like a decline in the radiative forcing which I would interpret as less heating and thus less energy accumulation and not as growth, as indicated in the diagram.

There seems to be some changes in the spectral distribution of solar irradiation though as described in 8.4.1.4.2 “Measurements of spectral irradiance” on page 690.

As UV heating of the stratosphere over a SC has the potential to influence the troposphere indirectly, through dynamic coupling, and therefore climate (Haigh, 1996; Gray et al., 2010), the UV may have a more significant impact on climate than changes in TSI alone would suggest. Although this indicates that metrics based only on TSI are not appropriate, UV measurements present several controversial issues and modelling is not yet robust.

and

A wider exposition can be found in Supplementary Material Section 8.SM.6.

which I havent found yet. Does this lead to the growth?

• John Baez says:

I don’t know the answers to all your questions, but it’s important to keep in mind that in the time period 1970-2014, the change in the power delivered to the Earth by the Sun has been tiny compared to other effects. It’s so small that the error bars in the graph below prevent us from knowing for sure whether the change is positive or negative.

So for understanding global warming during this period, this issue is unimportant… although it’s important to be sure it’s unimportant!

I don’t know how this graph was created. I could find out, but right now I’ll just point out this other graph:

which shows that changes in the power delivered to the Earth by the Sun are on the order of 0.1% during this time period. This graph is from Chapter 8 of the WG1 AR5 report, and the reasons for the discrepancies between the different curves are discussed there.

While the sunspot cycles are clearly visible, those will probably average out. The remaining secular variations in power is so small that it’s hard to tell by eye whether it’s positive or negative! So, this is not an issue I want to spend a lot of time on, given the overall urgency of global warming.

• arch1: Some quick answers. First, the ‘1860-1879″ reference period is correct. What that means is that this graphs is showing the net difference in energy inflow compared to what it was a century earlier (i.e. at the beginning of the industrial era).

The measurement of energy fluxes at the top of the atmosphere (including loss of energy back into space) are measured very precisely by several different satellite. So the difference between the two graphs has been measured fairly precisely – the biggest uncertainties are in the relative contribution of each forcing agent.

The dip in energy stored in the upper ocean is related to the very strong El Nino year of 1998. In strong El Nino years, the ocean releases heat, which means we get a very hot year (as measured in surface temperatures). This is also the cause of many of the myths around a warming “hiatus” over the last fifteen years. Because that heat was transferred to the land surface, it shows up as a big blip in surface temperatures, and if surface temperature is all you care about, it looks like the warming slowed with respect to a 1998 baseline. But as the first graph above shows, there is no slowdown. It’s just that we haven’t had a strong El Nino year since then. Projections show one developing in the Pacific right now, so we might have a remarkably warm year at the surface this year.

If the aerosol reductions look remarkably linear, that’s probably more an artefact of uncertainty more than anything. Aerosols have by far the largest uncertainty band, and contribute the biggest unknown to our estimates of climate sensitivity. Most of this comes from industrial pollution, especially from parts of the world that have weaker regulations on clean air (e.g. China). If countries like China take concerted effort to clean up their air (and I suspect they have no choice, given the public health impact), then this cooling effect is likely to diminish. If we wean ourselves off fossil fuels fairly rapidly, then it will diminish anyway, as most of this pollution is a byproduct of burning coal and oil.

• arch1 says:

Thanks much Steve. But re: the ’1860-1879″ reference period – if these really *are* comparisons w/ a century earlier, how is it that all of the line graphs miraculously converge to ~0 at t=1970?

John wrote:

it’s important to keep in mind that in the time period 1970-2014, the change in the power delivered to the Earth by the Sun has been tiny compared to other effects. It’s so small that the error bars in the graph below prevent us from knowing for sure whether the change is positive or negative.

But why has the mean curve been drawn in such a way that it reaches a positive cumulative energy of about $30\times 10^{21} J$ ?? That’s not nothing.

If there would have been a indecisiveness as you describe it then the mean curve should be the x-axis. As said the IPCC wrote about the solar cycle:

This very likely led to a small negative RF of –0.04 (–0.08 to 0.00) W m–2 between 1986 and 2008.

And indeed Figure 8.10. doesn’t “look” as if there are secular variations into the positive direction but rather in the negative. Did a change in the spectral distributions result in a positive forcing net effect? But then if this would be a secular change like towards shorter wave lengths it should also be visible in Figure 8.10. So again where does this $30 \times 10^{21} J$ come from?

• Nad: I’ll have to investigate, but I think the difference is due to different choice of baselines. The graph above is relative to 1860-1879. When it shows a positive solar RF, it means positive relative to the previous century. That can be entirely consistent with a negative RF relative to earlier in the 20th C.