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The IPCC (via Wigley et al) says there is a 50 percent probability that the world will warm by at least 3.06 degrees Celsius by 2100, and a 90 percent probability that the warming will be between 1.68 degrees Celsius and 4.87 degrees Celsius. I think there is a 50 percent probability that the warming in the lower troposphere will be less than 1.0 degree Celsius, and there is a 20 percent probability that the lower troposphere will actually be cooler in 2100 than it was in 2000.
When I write, "We will all die!*," I'm simply stating the historical truism that the only certain things are death and taxes. My asterisk (*) concerns the possibility raised by computer-guru/author/futurist Ray Kurzweil. Mr. Kurzweil is of the considered opinion that "humans" will obtain immortality in the 21st century. (Probably late in the 21st century, so this may only be of interest to you kids out there.) I put "humans" in quotation marks, because Mr. Kurzweil is also of the opinion that humans as we know them will be rendered obsolete in the 21st century. He thinks we will essentially choose to replace ourselves with human/machine blends, or even all machines...or even no particular form at all. Interesting stuff! But way off the topic of global warming, so if you're interested, go get Mr. Kurzweil's book, titled, "The Age of Spiritual Machines."
When I write, "We will all die...but almost certainly not from global warming" I'm referrring to my opinion about the future...as opposed to folks like the Intergovernmental Panel on Climate Change. Let's get down to it.
The extent of global warming is dependent on two things:
1) The buildup of greenhouse gases in the atmosphere, and
2) Feedbacks related to the buildup of greenhouses gases in the air.
Feedbacks related to the buildup of greenhouse gases in the air is pretty much beyond my field as an environmental engineer, so I'll focus on the buildup of greenhouse gases in the atmosphere.
Buildup of greenhouse gases: the IPCC view versus my view
Two techniques are available to estimate the future buildup of buildup of greenhouse gases in the atmosphere: 1) the "black box" approach, and 2) the incredibly-complicated-mechanistic-model approach. The "black box" approach works something like this: determine current trends, and assume that they'll continue, at least in the near future. The incredibly-complicated-mechanistic-model approach involves constructing one's own little "world economy," and predicting which countries' economies will expand, which will contract, what the changes in energy technology will be, and a whole lot of other things.
Recent trends in CO2 emissions and atmospheric concentrations
Let's start with emissions of carbon dioxide, and resultant atmospheric concentrations. Table 1 lists human emissions of carbon dioxide and resultant atmospheric concentration changes for the years 1960 to 2000 (Worldwatch, 2000). Table 1 also shows the decade-to-decade change in emissions, percentage change in emissions, and the resultant change in atmospheric concentrations. The decadal percentage changes in CO2 emissions are shown in Figure 1.
Table 1. CO2 Emissions and Atmospheric Concentrations, from 1960 to 2000.
| Year | CO2 (million tons) |
CO2 (ppm) | CO2
tons (% change) | CO2
ppm change | CO2
ppm (% change) |
|---|---|---|---|---|---|
| 1960 | 2,535 | 316.7 | 57 | 7? | 2.8 |
| 1970 | 3,997 | 325.5 | 58 | 9 | 2.8 |
| 1980 | 5,155 | 338.5 | 29 | 13 | 4.0 |
| 1990 | 5,931 | 354.0 | 15 | 15 | 4.6 |
| 2000 | 6,299 | 369.4 | 06 | 15 | 4.3 |
What can we tell from Table 1 and Figure 1? Well, first notice how the percentage change in emissions of carbon dioxide have almost completely plateaued. From 1950 to 1960, CO2 emissions increased by 57%. From 1960 to 1970, emissions increased by 58%. This is the characteristic of exponential growth...emissions increasing by a fixed percentage every decade. However, from 1970 to 1980, emissions increased by 29%. From 1980 to 1990, the increase was only 15%. And from 1990 to 2000, emissions only increased by 6%. And in fact, in 1998, 1999, and 2000, human emissions of CO2 actually declined. The implications of this plateauing in emissions of CO2 are huge.
If CO2 emissions have reached their peak, it means that CO2 concentrations can be expected to go up by a smaller and smaller percentage each decade. For example, from 1980 to 1990, CO2 concentrations went up by 4.6%, but from 1990 to 2000, concentrations only increased by 4.3%. Future decades will have even smaller percentage increases, if emissions have truly plateaued.
Recent trends in methane atmospheric concentrations
Now, let's look at methane concentrations in the atmosphere. The table below indicates atmospheric concentrations of methane, the 5-year change in atmospheric concentration, and the 5-year percentage change in concentrations. Again, just like the emissions of CO2, the concentrations of methane appear to be plateauing. From 1980 (not shown) to 1985, concentration increased by 4.4%. From 1985 to 1990, the increase was only 3.4%. From 1990 to 1995, the increase was only 2.1%, and from 1995 to 2000, the increase was only 1.3%. In each period, the percentage increase was lower. Atmospheric methane concentrations seem to be plateauing, and therefore shouldn't rise much in the future.
Table 2. Methane Atmospheric Concentrations, from 1985 to 2000.
| Year | Methane (ppb) | Change (ppb) | Change (%) |
|---|---|---|---|
| 1985 | 1637 | 70 | 4.4 |
| 1990 | 1693 | 56 | 3.4 |
| 1995 | 1729 | 36 | 2.1 |
| 2000 | 1752 | 23 | 1.3 |
So there we have it. CO2 emissions seem to have plateaued, and methane concentrations in the atmosphere seem to have plateaued. So that's what would happen if things stay on the trends they seem to be on right now. Now let's compare that to the IPCC projections for what's going to happen in the future. The IPCC projection don't use this "black box" approach, but instead use the "incredibly-complicated-mechanistic-model" approach. The details of the assumptions IPCC uses are so involved, that it makes more sense to simply look at their outputs, versus the "black box" outputs.
Methane: IPCC projections versus my projections
It turns out that the IPCC hasn't ever made probabilistic (i.e. probability-based) estimates of what CO2 emissions, CO2 concentrations, methane concentrations, and temperatures will be in the 21st century. Instead, they offer a series of approximately 40 "stories" (that's their word, not mine) of what could happen in the 21st century...without saying which of the "stories" they think is most likely to occur. In my opinion, this is...well, pathetic. (There, I said it.) What it does is allow the IPCC to make projections, without taking any real responsibility for their projections. Fortunately, there was a Science magazine article by some IPCC scientists (Tom Wigley et al) that contained 5%, 50%, and 95% probability projections for warming in the 21st century. What "5% probability" means is that there is, according to Wigley et al.'s interpretation of IPCC projections, only a 5% chance that the value (for CO2 or methane content, or for temperature) is below the value given. In other words, if the 5% probability value for CO2 concentration in 2030 is 423 ppm, that means they think there is only a 5% probability that the CO2 concentrations in 2030 are going to be below 423 ppm. Anyway, for simplicity's sake, I'm going to take those 5%, 50%, and 95% probability projections, rather than dealing with the 40-odd projections (with no assigned probabilities) made by the IPCC.
Based on Wigley et al., let's look a methane atmospheric concentration predictions from the IPCC, in Table 3, below:
Table 3. IPCC Projections (from Wigley et al) for Methane Atmospheric Concentrations in 2060.
| Year | 5% probability | 50% probability | 95% probability |
|---|---|---|---|
| 2060 | 1800 ppb | 2490 ppb | 2800 ppb |
| 2060 | 8 ppb/ decade | 123 ppb/ decade | 175 ppb/ decade |
From the table above we see that the IPCC (via Wigley et al) thinks the 50% probability value for methane concentration, in the year 2060, is 2490 ppb. Since the 2000 value (see previous table) was 1752 ppb, this is an increase in concentration of 738 ppb, in the 6 decades from the year 2000 to the year 2060; that represents an increase of 123 ppb per decade, as shown in the table above. But lets compare the IPCC "50% probability" projection with recent history. As shown in the previous table, from 1995 to 2000, methane concentration only increased by 23 ppb (or 46 ppb per decade). In other words, the IPCC says there is a 50% probability that methane concentrations will have an average increase of 123 ppb from 2000 to 2060, even though the change from 1995 to 2000 only represents a decadal increase of 46 ppb. In a word, the IPCC's methane atmospheric concentration projection is nonsense. There is virtually no chance (well, almost certainly less than a 5% chance) that methane concentrations will increase by 123 ppb per decade from 2000 to 2060, but the IPCC is saying there is a 50% chance that methane concentrations will increase by an average of 123 ppb per decade for that period. Once again, this is simply nonsense. And since the methane concentration projections are nonsense, they also push the IPCC's temperature projections towards nonsense...since the IPCC's temperature projections are based, in part, on the methane concentration projections.
What would I propose as an alternative, if the IPCC projections are so unrealistic? Using the "black box" approach, my "50% probability" projection would be that methane concentrations in 2060 would be somewhere between the current concentration (1752 ppb) and 1890 ppb (which represents the current 1752 ppb, plus 23 ppb per decade, times 6 decades). That would be about 1820 ppb, for my "50% probability" projection.
My "5% probability" and "95% probability" projections for methane concentrations would be more speculative. Just taking a wild stab, I'd estimate that there's a 5% probability that methane concentrations in 2060 will be below 1600 ppb, and a 95% probability concentrations will be below 2000 ppb.
Let's look at the IPCC projections, versus my projections, in Figure 2.
Notice how the IPCC 50% and 95% probability curves are ridiculously high, when compared with the trend from 1985 to 2000. In fact, the IPCC 5% probability curve is almost exactly coincident with my 50% probability curve! And the IPCC 50% probability curve is much higher than my 95% probability curve. For example, the IPCC is saying there is a 50/50 chance (1 in 2 chance) that the methane atmospheric concentration will be above 2490 ppb in 2060; my prediction is that there will be less than a 1 in 20 chance that atmospheric methane concentration will even be above 2000 ppb in 2060. Clearly, someone's predictions are very wrong. And the trend for 1985 to 2000 sure makes it look like the IPCC projections are the ones that are wrong.
CO2: IPCC projections versus my projections
But let's look at the CO2 projections from the IPCC. Perhaps they just goofed on the methane projections, but the CO2 projections are justifiable?
First, we'll look at IPCC projections for CO2 emissions. Those are in Table 4. As can be seen from Table 4, the 50% probability emission level in 2060 is 15,000 million tons of carbon (i.e., 15 billion tons of carbon). But if we go back to the trends from Table 1 and Figure 1, we see that this prediction is simply wacko. (To use a scientific characterization.) From Table 1, we see that the emissions in 2000 were only 6,299 million tons. And from Table 1 and Figure 1, we see that those emissions only increased by 6 percent from 1990 to 2000. But the IPCC says there is a 50% probability that CO2 emissions will increase to 15,000 million tons by 2060! No way, Jose! (Another scientific phrase.)
Table 4. IPCC (via Wigley et al) Projections for CO2 Emissions (millions of tons of Carbon)
| Year | 5% probability | 50% probability | 95% probability |
|---|---|---|---|
| 2060 | 8,500 | 15,000 | 25,000 |
| 2100 | 4,500 | 16,200 | 29,000 |
In fact, even the 5% probability value given by the IPCC for 2060 looks like it might be high. They predict 8,500 tons per year in 2060. Year 2000 emissions were 6,299 million tons, increasing by 6% from 1990 to 2000. If we project 6% per decade increases, from 2000 to 2060, we get emissions of 8,940 million tons in 2060. But if emission have truly plateaued, the value in 2060 would be less than or equal to the current 6,299 million tons.
My predictions, based on a "black box" approach, would be that the 50% probability level of emissions in 2060 would be about 5,000 million tons, or about 20% less than emissions in 2000. Even my guess for 95% probability emissions in 2060 would be 12,000 million tons...or less than the 50% probability emissions given by the IPCC. My guess for 5% probability emission would be 3,000 million tons.
Figure 3 shows IPCC projections, and my projections, for CO2 emissions for the 21st century.
Once again, as in Figure 2, the IPCC projections for "50% probability" and 95% probability are completely unrealistic. Look at those curves don't match up at all with the trend from 1970 to 2000. Only the IPCC curve for "5% probability" is even halfway realistic.
Since the IPCC projections for CO2 emissions are completely unrealistic, it stands to reason that the IPCC projections for CO2 concentrations in the atmosphere will also be completely unrealistic. But let's look at them, anyway. Table 5, below, shows the IPCC CO2 atmospheric concentration projections:
Table 5. IPCC Projections (via Wigley et al) for CO2 Atmospheric Concentrations in 2030, 2060, and 2100.
| Year | 5% probability | 50% probability | 95% probability |
|---|---|---|---|
| 2030 | 423 ppm | 438 ppm | 452 ppm |
| 2030 | 18 ppm/decade | 23 ppm/decade | 27 ppm/decade |
| 2060 | 490 ppm | 560 ppm | 620 ppm |
| 2060 | 20 ppm/decade | 32 ppm/decade | 36 ppm/decade |
| 2100 | 540 ppm | 720 ppm | 980 ppm |
| 2100 | 17 ppm/decade | 35 ppm/decade | 61 ppm/decade |
From Table 5 above, in the year 2030, we see a "5% probability" prediction of a CO2 atmospheric concentration of 423 ppm. Since the concentration in the year 2000 was approximately 369 ppm (see Table 1), that represents an increase of 54 ppm in 3 decades, or 18 ppm per decade (18 ppm/decade). But let's look at the previous few decades, from Table 1. From 1970 to 1980, the CO2 atmospheric concentration increased by 13 ppm. From 1980 to 1990, the CO2 atmospheric concentration increased by 15 ppm. And from 1990 to 2000, the CO2 atmospheric concentration also increased by 15 ppm. In other words, the IPCC says that there is only a 5% chance that CO2 atmospheric concentrations will increase by less than 18 ppm per decade from 2000 to 2030...even though atmospheric CO2 concentrations have never increased by more than 15 ppm in a single decade. And the IPCC "50% probability" value is even more ridiculous; the IPCC "50% probability" prediction for 2030 is 438 ppm, representing an increase of 23 ppm per decade!
And the numbers get even more ridiculous for the year 2060. And even more ridiculous than that in 2100. The IPCC's 5% probability value for 2060 is 490 ppm, which represents an increase of 20 ppm/decade. But once again, from Table 1, there has never yet been a decade when the concentration has increased by more than 15 ppm. So the odds of the concentration increase averaging 20 ppm/decade over the next 6 decades is virtually zero; yet, the IPCC is saying that there are 19 chances out of 20 that atmospheric CO2 concentration will increase by at least 20 ppm/decade for the next 6 decades. That's just complete nonsense. One wonders why IPCC scientists would even be paid to generate such complete bunk.
My own prediction, based on the black box idea of following current trends, would be that concentrations will increase by 15 or 16 ppm/decade for the next 2-3 decades. Then, because emissions have plateaued and will start downward, the atmospheric concentration increases will also start to go down. Figure 4 compares my projections with IPCC projections.
Figure 4 is interesting in that the deviation of IPCC projections from current trends isn't so obvious, as with the CO2 emissions projections in Figure 3. In Figure 3, the IPCC's 95% probability curve sticks up from recent trends like a cowlick. In contrast, in Figure 4, the deviation of IPCC's projections from current trends isn't nearly as obvious.
The Punchline: IPCC Temperature Projections (via Wigley et al) Versus My Temperature Projections
All this discussion of the ridiculousness of IPCC's methane concentration and CO2 emissions projections has probably just bored non-technical readers. (And perhaps technical readers, too.) But it was all necessary to set up why the IPCC's temperature projections are hogwash. The IPCC's temperature projections for the 21st century are completely unbelievable, precisely because their projections for methane atmospheric concentrations, CO2 emissions, and resultant CO2 atmospheric concentrations are all hogwash. In order for the IPCC to generate believable temperature projections, they will have to change their projections for methane atmospheric concentrations, CO2 emissions, and resultant CO2 atmospheric concentrations.
Table 5 contains the IPCC Third Assessment Report projections for temperature increases in the 21st century (i.e., 2030, 2060, and 2100), relative to the year 1990.
Table 5. IPCC Projections for Temperature Increases, Relative to 1990, in Degrees Celsius.
| Year | 5% probability | 50% probability | 95% probability |
|---|---|---|---|
| 2030 | 0.48 | 0.80 | 1.17 |
| 2030 | 0.12/decade | 0.20/decade | 0.29/decade |
| 2060 | 1.29 | 2.17 | 3.34 |
| 2060 | 0.16/decade | 0.27/decade | 0.42/decade |
| 2100 | 1.68 | 3.06 | 4.87 |
| 2100 | 0.15/decade | 0.28/decade | 0.44/decade |
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