In early December I wrote a post called "2014 will not be the warmest year on record, but global warming is still real." The very first thing I said in that post is that I was going out on a limb. I also discussed whether or not one year mattered, and I discussed the nature of the phrase "X is the Yth warmest year on record," going into details on what "the record" is and how we measure this.
I want to reiterate something very important that I mentioned then. Here, we are talking about a combination of measurements from the sea surface and the air just over the land (about where your head is when you are walking around). Changes in this surface measurement over time reflect less than about 5% of the overall changes in temperature experienced by the Earth because of the addition of greenhouse gasses to the atmosphere (or reduction of "sinks" of those gasses, or of heat) by human activity. Most of the additional heat goes into the ocean.
The reason I was conservative in my earlier post was to avoid a situation where we (climate scientists, climate science communicators, etc.) made statements about 2014 that turned out to be wrong in a subset of the records, of which there are several. That is still possible, I suppose. But, now that we are past the middle of December, it is possible to estimate December's overall temperature, add that to the prior 11 months, and say with much more certainly that 2014 will be the warmest year.
My friend and colleague John Abraham has been doing just this. He's been collecting data on daily temperature estimates (I helped a bit, covering that task when he was overseas and unable to do so himself). He then took this information and, essentially, asked himself the same question every day: "Do I have enough data to call this?" Over the last several days NASA and NOAA have updated their temperature records for November, and NOAA came out with an analysis showing how difficult it would be for 2014 to NOT be the warmest year in their records. When John Abraham combined his analysis with the data through November, he decided, yesterday, that it was time to call it.
...2014 will be the hottest year ever recorded.
I can make this pronouncement even before the end of the year because each month, I collect daily global average temperatures. So far, December is running about 0.5°C above the average. The climate and weather models predict that the next week will be about 0.75°C above average. This means, December will come in around 0.6°C above average. Are these daily values accurate? Well the last two months they have been within 0.05°C of the final official results.
The graph above shows the NASA data by year, in standard units (0.01 Celsius anomaly using a base period of 1951-1980) with John's estimate for 2014 added to the end. This will change slightly after NASA gets the December data out.
Remember, this is the instrumental record, which goes back into the 19th century. But when we look at proxyindicator data for previous centuries or millennia, we don't see any evidence suggesting that there were any, or if there were any, that there were many, years that would have been warmer for a very long time. That goes back through the entire Holocene. Before that, it is harder to make that claim. There is a good record over the last several glaciations, say bout 800 thousand years or so, for which we can say that the present level of global surface temperature is in the range of the warmest periods, or at the top end of the range. This becomes less likely as we go back in time, as there has been a general cooling of the earth (with a lot of ups and downs) since some time in the Miocene (over 5 million years ago).
However, paleorecords together with basic physics tell us that the current level of CO2 in the atmosphere should associate with a much higher temperature than we experience now. This is why the Earth's surface temperature is going up. The added CO2 is a little like adding fire to the bottom of a pot f water. The water will eventually reach boiling point, but it will take some time. Because of the way heat (and to some extent, added CO2) circulate among the various reservoirs on the Earth's surface, a process that might take a geological instant on a simpler planet (rocky surface, no significant water including no significant oceans, simple Nitrogen atmosphere) takes much longer. We are not sure how warm the Earth will get with 400ppm CO2, which is about where we are now, but it is quite a bit more than the present temperature. That number, even if it is on the low end of the possible range, likely exceeds ancient temperatures for very long time. The fact that we are continuing to add CO2 to the atmosphere, and even them most intense efforts to reduce this are going to take time, means that we can expect a much higher concentration of CO2, and thus, an even higher eventual level of warming. Over coming decades, we will be recording "warmest years" that are warmer than anything in millions of years.
Also, there are at least two additional factors that must be taken into account. One, perhaps most important, is that the rate of change we are currently experiencing is high, perhaps unprecedented in many millions of years. Rapid rates of change is bad. Second, and in part a subset of the first (but not perfectly) is the problem of circumscription of our agriculture and infrastructure, as well as natural preservation areas. When they build roads in Mississippi vs. Minnesota, they build them differently because of the climate. As the climate warms, the old roads turn out to be built wrong and have to be redone to handle a different range of temperatures. That's a small problem, because we rebuild our roads now and then anyway. Because of changes in temperature and rainfall patterns, the irrigation infrastructure for agriculture will become inappropriate to the task in some regions. That is a larger problem. As warming occurs, parasites from southerly areas move north, and find populations of plants and animals that are not adapted to them. Forests die, large mammals go locally extinct, etc.
Slowly slowly, we are getting to the point where it might be safe to bring back some of the dinosaurs! (Except they would starve because the plants the herbivores eat are rare or extinct. The carnivores could find food, though, I suspect...)
Greg, where do you get the daily temperature records?
Even the deniers of the evidence that Earth is warming anomalously, who emphatically insist it is not doing so, know that it is. How else can one explain why they have all, without exception, ref8used to take my US$1,000 that defends the proposition that a new record high global average temperature will be set by end of year 2018? Deniers do not believe what they claim to believe.