The US in a High Emissions Scenario

Number of days annually over 100^oF in the recent past, and under high emissions in 2080-2099 according to p90 of Global Climate Change Impacts in the United States

So, I ended up spending much of my weekend going through Global Climate Change Impacts in the United States, and I have to say I'm pretty gutted by the experience.  I'm just amazed that I didn't know about this report, despite regularly reading the NYT and a variety of progressive and moderate-conservative blogs at the time it was issued.  Realclimate never mentioned it.  Grist covered it, and the NYT did in fact mention it, but the NYT story has a flavor of "the government released a big long boring report with nothing new in it" and Grist mostly posts a long video of the press conference with little clue as to why you should watch it.  And neither coverage item, had I seen them, would have given me the slighest clue at how dynamite some of the contents are once I started reading and thinking for myself.  I think this report should be far higher profile in the public discourse than it is.  In fact, every citizen ought to read it.

Let me try to go through a few of the things that seemed particularly significant to me.  At some abstract level, I knew most of this stuff, but the maps and charts in here really made the scale of the problem much more clear to me.

Firstly, the report is written by a large collaboration of 30 or so authors, and a slew more reviewers, drawn from a variety of US agencies, with NOAA as the lead.  So it's in the character of an official US government assessment of the science, addressed to the President and Congress.  There are 500+ references, and it is in turn based on a series of scientific synthesis reports prepared by various agencies.  So it's clearly a summary of an enormous amount of work by a very large number of scientists and represents the state of the art in current understanding of climate change as applied to the US.  This is not to say that it will be right in all respects - clearly the planet as an entire system is so complex that scientists may not have successfully understood and modeled all the important physics, chemistry, and biology, and there may be surprises as additional effects show up.  Anyone paying attention to climate science is aware that there have already been significant surprises - it turned out that the Greenland and West Antarctic ice sheets started melting much faster than had been expected, and the Arctic sea ice appears to have been melting faster than climate scientists expected.  So I don't dismiss the possibility of things either being better or worse than climate science currently predicts.

Still, it seems worth while really understanding humanity's best guess about what the situation is.  Given that emissions are growing faster than the IPCC has studied, that the world has been unwilling or unable to agree on any meaningful global treaty, with the largest emitters, China and the United States, in particular unwilling to make any meaningful attempt to limit emissions, I wanted to look at the question "How bad are things in a high emissions scenario?"  In particular, in this post, I look at the period 2080-2100.  My children were born in 2000 and 2002, so 2080-2100 represents the likely end of their lives, all being well.  So this is a summary of the changes they will experience over the course of their lives.

Let's start with the figure from up top (a slight rearrangement of one on p90 of the report) which looks at how many days of the year the temperature reaches over 100^oF:

Number of days annually over 100^oF in the recent past, and under high emissions in 2080-2099 according to p90 of Global Climate Change Impacts in the United States

You will note the spread of the red/orange, in which you have 3-4 months-worth, or more, of days over a hundred degrees, from a small area of inland southern California, Nevada, and Arizona to most of the United States - at least California's central valley, most of the mountain west, the great plains and Texas, all but the northernmost sections of the mid west, and most of the south east.

Let's look a little bit at the area that has been red/orange in the recent past to get more of a feeling for what that's like.  I found a nice map at the Arizona-Sonora Desert Museum:

So clearly, the region we are talking about, where temperatures have historically been over 100F for 90-100 days or more, is the Sonora and Mojave Deserts.  Let's have a few visuals:

The Sonora desert from here.

The Mojave desert from here.

Hmmm.  But, obviously, these places are deserts now not just because it's hot, but because it's dry, right?  If it was this hot but wet, it would be a jungle, not a desert.  True enough.  Here's annual precipitation in the United States (from here).

Indeed, you can see that the Sonora/Mojave deserts are places that get less than 10 inches of rain each year.  Of course, there's a lot of the west that's similarly dry, or only a little bit wetter.  Ok, so what's going to happen to US precipitation under high emissions?  Now we turn to p31 of the report:

So basically, in the winter, the northern half of the country gets more rain/snow, while the southern half gets less rain.  But in the summer, the whole country will get less rain, and in the case of the Pacific Northwest and the Southeast, a lot less rain.

So, roughly, summers are going to be completely hellish to be outside throughout a lot of the country - comparable to conditions in the Sonora/Mojave deserts now.  The desert areas of the southwest are going to undergo a major expansion in all directions, the dry-mediterranean climate of Northern California is going to push up into Oregon and Washington, while California itself increasingly desertifies, the southeast is going to get much dryer and hotter, etc, etc.

I think it should be obvious that under these circumstances, just about every landscape in the country is going to change radically.  For those of us who like to get out and hike/bike/kayak, there's just about no place you might love that isn't going to undergo massive wrenching change.  For example, on p81, we see the Eastern half of the country, under a mid range warming scenario (so on the present trajectory, it's likely worse than this):

So fall in New England is not going to be the same at all, and maple syrup will become a Canadian product.

Furthermore, since trees can't up and walk, the process of changing forest types this fast isn't going to be a smooth one.  Instead, it will be mediated by fire and pests destroying the forests in the wrong place, and then invasive opportunistic plants springing up in their place (see p82-83 for more unpleasant detail).  So all the work that's been done over the past century to preserve some wild ecosystems in national parks etc, is going to be mostly subverted.  The park may still be there, but what grows in it will, in most cases, be nothing like the thing that we were originally trying to save.

How does one talk to ones kids about this stuff?