While at the annual American Physical Society meeting in Denver CO last week, I had a chance to listen to a few talks about the current state-of-the-art in climate change modeling. There were several informative talks, about the role of clouds (uncertain), better modeling climate sensitivity, and modeling sea ice, but most intriguing was a talk by Judith Curry about the growing divergence between what are are actually observing and what climate models are predicting in terms of global temperature changes.
The main issue here is that actual observations of global mean surface air temperatures show no increase since about 1998, shown in the figure above based on four of the main climate data centers. According to Curry, this no longer matches contemporary climate models within a 2% confidence window, indicating our models are missing something! Climate change skeptics immediately jump on this finding as evidence that climate change is a hoax, which is NOT the right way to think about this! On the other side, Judith Curry herself has come under some scrutiny from other science bloggers accusing her of disseminating erroneous information and cherry picking data.
I guess I come in on this somewhere in between – people like Judith Curry are important in that it forces climate scientists to analyze the data in a way that can justify their arguments – I feel that this can only help in the climate change discussion. Which they can do, I might add! A great example is this blog post, which discusses the fact that, if we only look at temperature data from before 1998, and use that data to predict what temperatures will be from 1998-present using linear regression, we actually find that most years from 1998-2013 are above the linear prediction! This is because temperatures actually rose very quickly before the so-called hiatus or pause, so that even when temperatures aren’t changing, they fit better to the linear regression of increasing temperatures than a model predicting no change. A quick description, but please read the excellent blog post to understand it completely.
So it’s very important to understand the data correctly – the planet is still warming! Now, we can still see that the temperature change has leveled off over the past decade or so, and I think it’s interesting science to explore what might be causing this. A recent Science Perspective, “The Tropical Pacific Ocean – Back in the Driver’s Seat“, provided a valuable overview of the current research into this.
Basically, we know several feedback systems that can reduce warming, but we can’t model them precisely enough yet to know exactly when this will occur. One such example is aerosols, which are particulates of matter that are a consequence of pollution. These particles float into the atmosphere and more importantly into clouds, where they promote condensation of water around the particles (nucleation). This leads to more particles for incoming sunlight to scatter off, which leads to reduced warming. In the mid 20th century, a cooling period was observed that is now attributed to a large release of sulfate aerosols. This cooling trend stopped in the 1970’s when pollution constraints were mandated in developing countries.
Other factors are important, such as cirrus clouds, water vapor concentration, solar output variability, which we all need to understand better. But one intriguing finding recently may provide an important clue into a different cooling mechanism. Although most of the globe is feeling much increased temperatures, the tropical Pacific is currently colder than any other time in the late 20th century. Models that include this can account for the current warming break. More importantly, further models show that a cold Pacific stores more heat deeper below the surface, and that this is part of natural climate variability. This means that this will not last forever, and warming will continue again!
It’s important that the climate science community does not become as entrenched in fighting against consensus as climate change skeptics are. I welcome scientists such as Curry to throw skepticism at the data, which will challenge other scientists to find a response or adjust their conclusions if necessary. Data HAS NOT supported the claim that global warming has stopped, as simply seen from the graph above, but I believe Curry’s argument is more to state that we still need to understand more about the climate to understand these variations we see. This type of statement is dangerous when in the hands of others who are more close-minded, and use her words to fight their preconceived agenda. But science can and will continue to explain the unexpected data as they arise in an objective manner, and we will continue to be honest about our conclusions.
Clement, A., & DiNezio, P. (2014). The Tropical Pacific Ocean–Back in the Driver’s Seat? Science, 343 (6174), 976-978 DOI: 10.1126/science.1248115