Hacker News Reader

Comment by zackmorris | Hacker News Reader

Of course the cause is global warming. This is one effect, but another is the Rocky Mountain rain shadow over the midwestern US:

https://news.climate.columbia.edu/2018/04/11/the-100th-merid...

For decades most of us have assumed that the warm zone over the tropics would get wider, driving desertification towards the poles. But what's more likely is that the rain shadow effect will work along the east-west axis with the prevailing winds over each region of the world.

So the US will lose the Dakotas, Nebraska and Kansas as they acquire the precipitation level of Wyoming. Arguably Oklahoma and Texas are on the cusp now. The Ogallala aquifer will get pumped dry even faster as the breadbasket states reach harder for irrigation in desperation. Basically the drought that states like Nebraska are experiencing now is going to be the new normal on a long enough timescale (a few decades at most).

View on HN

Question: will the amount of moisture in the air remain at a net neutral balance? If so, will the precipitation fall elsewhere? What areas do we expect to get more precipitation? What borderline arable lands will become arable as a result of climate change, if any?

Good question! Unfortunately, the answer to your first question is no. Higher temperature air can "hold" more moisture than cooler temperature air. And for a fun double whammy, higher temperatures also increase ground evaporation, drying out the soil and holding that water vapour in the air.

Now, you could generally assume that all that air eventually has to condense somewhere, but the problem is that we've now raised the potential threshold of what precipitation entails. So we've got drier soil (which is worse at holding moisture when it rains), more potential for precipitation, and a longer buildup time between precipitation threshold events. We've just created feedback loop that encourages flash flooding, making it more difficult to farm all areas, both old farmland and new potentially arable land.

Its fun to learn about the complex system dynamics of climate physics, it'd just be more fun if it didn't come with a side serving of impending catastrophe.

Triple whammy. Water vapor is another greenhouse gas, pretty powerful as it.

And probably it will have local climate effects if not global ones.

And then when it does rain the ground is so dried out that the rain runs right through the topsoil into the layers beneath.

The IPCC regional fact sheets from AR6 showing expected changes in precipitation are at https://www.ipcc.ch/report/ar6/wg1/resources/factsheets. For example, the fact sheet for North America is at https://www.ipcc.ch/report/ar6/wg1/downloads/factsheets/IPCC....

Many areas are in fact predicted to have increased precipitation.

It'll fall somewhere eventually. Where, is a complex topic that I don't think anyone has the answer to (we can barely predict the weather for a few weeks).

> What borderline arable lands will become arable as a result of climate change, if any?

Anywhere with water will experience forestation. With higher CO2 levels, the earth will definitively become greener. But don't hold your breath for humans (pun intended).

It’s easier to predict rainfall patterns over decades than weather over weeks.

for every degree the atmosphere warms it can hold 7% more water, and a recent study confirmed that it does. apparently the distribution is not even but in general we are approaching a wetter and warmer climate.

A lot of the western US is going to be much harder to live in. Desertification, lack of clean drinking water, and heat being the major issues. The midwest is going to get a lot more crowded in the coming decades and that's before all the climate refugees from around the globe start really pouring in.

Reply on news.ycombinator.com