Ocean Hot and Hotter StillThe eight articles in the preceding series, linked at the bottom, were originally motivated by the need to understand the discrepancies between the observed warming of the surface and the projected warming from climate models. Ultimately the articles evolved to a description of a range of activities that need to be addressed to quantify our representation of “short-term” climate variability. Short term, here, means 2 -30 years, or at most, less than a century.
The preceding articles highlighted some of the differences and likenesses between
weather forecasting and climate projections, keeping in mind we desire to make climate forecasts. In order to do a good climate forecast we will have to consider not only the natural variability that occurs from the motions of the ocean and atmosphere (
BW8), but also how the composition of the atmosphere changes (
BW6,
BW7), how the Sun varies, and how energy moves around (
BW3,
BW5); that is, between the air, the ocean, ice, and ground. There is also the critical need for more complete observations of the ocean and, in some cases, time – time to develop the observational and theory foundation to quantify how the land, ocean, ice, and air interact with each other.
A question: this is for the weather savvy readers of WU. Do you think that weather forecasts are good? Or bad? Do you think that they have gotten better over the past 20 years? Since it is hurricane season, do you look at those cones that show where a hurricane might go? It is my feeling that over the past 20 years that weather forecasts have gotten a LOT better. Observations have gotten better, models have gotten better, and how we use observations has improved in amazing ways. My point - yes, I am tediously making points lately - 20 years ago weather forecasts were quite useful. In fact, they were useful 40 years ago. Projections of climate change do not have to “wait” until all of these observation and theory issues are resolved to be useful. Like weather forecasting, we develop a system that is useful, actionable, and it improves over the years as we learn more and more.
The ocean has different roles in weather and climate forecasting. Because weather forecasts are of only a few days length, the primary role of the ocean is to provide “information” to the atmosphere. That is, the ocean influences the temperature and the amount of water in the atmosphere (
BW3). In a climate forecast, however, you have to consider how the ocean and atmosphere interact with each other. For example the ocean can take heat away from the surface and store it below the surface. The ocean can give up heat to warm the land. If weather patterns change, then the way the atmosphere drives the surface currents, such as the Gulf Stream, changes. The ocean takes up and releases greenhouse gases. In even a short-term climate forecast, the ocean becomes part of the forecast. (Again, this is why it is the proverbial red herring to imagine that climate forecasts follow from ever longer weather forecasts. That is an argument of simplistic, negligent convenience.)
There are two papers that I want to highlight here. The first is a recent paper by
John Lyman and co-authors, and is entitled “
Robust Warming of the Global Upper Ocean.” It appeared in
Nature. This paper takes a systematic look at recent warming in the global ocean. The point is made that ocean heat content, the amount of infrared radiation leaving the Earth, sea level rise and ice melting all need to balance. So a seeming problem is that for the past few years (since, say, 2003) the sea surface temperature has remained more of less constant, but sea level has continued to rise. Recall that when the ocean gets warmer it expands, and that causes sea level to rise. Sea level can also rise from the melting of glaciers and ice sheets. Because it takes less energy to melt ice than to heat and expand sea water, when we bring into the accounting the amount of energy entering and leaving the Earth, we are left with something of an imbalance. And when there is an imbalance, then there is evidence that we are not thoroughly sure what is going on.
The near constancy of the sea surface temperature and the apparent leveling of the increase in ocean heat content also occur at a time when the methods of taking the temperature of the ocean changed and became more complete. This is one of the challenges of climate science, and in fact, any scientific investigation that relies on long-term measurements. (Long-term? Above I said I was looking at short-term climate, a few years to decade. Well long-term when we refer to temperature data might, for the present purpose, be long enough to measure accurately short-term climate! Long-term measurement might refer to long compared with the technology used to make the measurement, long compared to how long a temperature instrument manufacturer is in business, or, just to make it interesting, long compared to the government or private contract that buys the low-bid vendor with technology that “meets the requirements.”)
When the new temperature measuring system comes into operation a lot of things happen, but almost always there is an inconsistency between the old data record and the new data record. Calibration of the observing system is required. Something else often happens with a new observing system. If measurements are made that go deeper in the ocean, higher in the atmosphere, or there are simply more measurements that cover the globe more completely, a bias between old and new data record can occur. Again there is the need to calibrate the observing system. What Lyman et al. do is to examine all of the published treatments of the data, as well as to analyze trends with several different methods. Their conclusion is that there is a robust (meaning statistically significant) trend from 1993 – 2008 of 0.64 Watts (unit or energy) per meter^2 (unit of area). If they break their analysis down and only look from 1993- 2003, the trend is almost the same as for the record as a whole. Therefore, this paper confirms an earlier suggestion that any “missing heat” is likely in the ocean (
BW3,
BW5).
That brings me to another paper that I find especially interesting, by
Gil Compo and
Prashant Sardeshmukh. The paper is entitled “
Oceanic influences on recent continental warming,” and appeared in
Climate Dynamics. This paper takes a stab at trying to understand the cause of observed warming on land, and in particular, is the warming directly traceable to local warming by greenhouse gases or through some other path? This is model study, and its results are subject to many uncertainties of models and experiment design. That said, they find that much of the “recent warming” observed on land can be traced to heating from the ocean. Recent is, more or less, the last half of a century, fifty years. They trace the heating of the land to increases of heat in the ocean. Their analysis cannot, standing alone, say the heating of the ocean is due to greenhouse warming of the planet.
That said, there is
other evidence that the heating of the ocean is attributable to greenhouse gas warming. With that, it suggests that the extra energy held at the surface due to increasing greenhouse gases serves to warm the ocean and then there is warming of the land. This does provide, intuitively, something of a moderating influence on warming of the land. It suggests, however, that heating of the ocean does not “harmlessly” carry away the extra energy, and that because of the large heat capacity of the ocean, warming will be with us for a long time (
Warm for 1000 years). We are not living in a rapidly, self correcting climate.
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Bumps and Wiggles (1): Predictions and Projections Bumps and Wiggles (2): Some Jobs for Models and Modelers (Sun and Ocean) Bumps and Wiggles (3): Simple Earth Bumps and Wiggles (4): Volcanoes and Long Cycles Bumps and Wiggles (5): Still Following the Heat Bumps and Wiggles (6): Water, Water, Everywhere Bumps and Wiggles (7): Blackness in the Air Bumps and Wiggles (8): Ocean, Atmosphere, Ice, and Land And here is Faceted Search of Blogs at climateknowledge.org