Click here to read the executive summary.

From The World Bank:

Key Findings

Water scarcity, exacerbated by climate change, could cost some regions up to 6% of their GDP, spur migration, and spark conflict.

The combined effects of growing populations, rising incomes, and expanding cities will see demand for water rising exponentially, while supply becomes more erratic and uncertain.
Unless action is taken soon, water will become scarce in regions where it is currently abundant – such as Central Africa and East Asia – and scarcity will greatly worsen in regions where water is already in short supply – such as the Middle East and the Sahel in Africa. These regions could see their growth rates decline by as much as 6% of GDP by 2050 due to water-related impacts on agriculture, health, and incomes.

Water insecurity could multiply the risk of conflict. Food price spikes caused by droughts can inflame latent conflicts and drive migration. Where economic growth is impacted by rainfall, episodes of droughts and floods have generated waves of migration and spikes in violence within countries.

The negative impacts of climate change on water could be neutralized with better policy decisions, with some regions standing to improve their growth rates by up to 6% with better water resource management.

Improved water stewardship pays high economic dividends. When governments respond to water shortages by boosting efficiency and allocating even 25% of water to more highly-valued uses, such as more efficient agricultural practices, losses decline dramatically and for some regions may even vanish.

In the world’s extremely dry regions, more far-reaching policies are needed to avoid inefficient water use. Stronger policies and reforms are needed to cope with deepening climate stresses.

Policies and investments that can help lead countries to more water secure and climate-resilient economies include:

Better planning for water resource allocation

Adoption of incentives to increase water efficiency, and

Investments in infrastructure for more secure water supplies and availability.

From Forbes.com (Ethan Siegel). Click through and read the whole article. Here’s an excerpt:

Modeling the Earth’s climate is one of the most daunting, complicated tasks out there. If only we were more like the Moon, things would be easy. The Moon has no atmosphere, no oceans, no icecaps, no seasons, and no complicated flora and fauna to get in the way of simple radiative physics. No wonder it’s so challenging to model! In fact, if you google “climate models wrong”, eight of the first ten results showcase failure. But headlines are never as reliable as going to the scientific source itself, and the ultimate source, in this case, is the first accurate climate model ever: by Syukuro Manabe and Richard T. Wetherald. 50 years after their groundbreaking 1967 paper, the science can be robustly evaluated, and they got almost everything exactly right.

If there were no atmosphere on Earth, calculating the climate would be easy. The Sun emits radiation, the Earth absorbs some of the incident radiation and reflects the rest, then the Earth re-radiates away that energy. Temperatures would be easily calculable based on albedo (i.e., reflectivity), the angle of the surface to the Sun, the length/duration of the day, and the efficiency of how it re-radiates that energy. If we were to strip the atmosphere away entirely, our planet’s typical temperature would be 255 Kelvin (-18 °C / 0 °F), which is most definitely colder than what we observe. In fact, it’s about 33 °C (59 °F) colder than what we see, and what we need to account for that difference is an accurate climate model.

The number one contributor, by far, to this difference? The atmosphere. This “blanket-like” effect of the gases in our atmosphere was first discovered nearly two centuries ago by Joseph Fourier and worked out in detail by Svante Arrhenius in 1896. Each of the gases present has some amount of absorptive effects in the infrared portion of the spectrum, which is the portion where Earth re-radiates most of its energy. Nitrogen and oxygen are terrible absorbers, but good ones include water vapor, methane, nitrous oxide, ozone and carbon dioxide. When we add (or take away) more of those gases from our planet’s atmosphere, it’s like thickening (or thinning) the blanket that the planet wears. This, too, was worked out by Arrhenius over 100 years ago.

But a true climate model is more complex, because there’s more at play than just the atmosphere. The oceans ensure that the amount of water vapor (and cloud cover, which impacts temperature significantly) change dependent on conditions, and if you tinker with one component of the atmosphere — like carbon dioxide, for instance — it impacts the concentrations of other components. Scientists refer to this general process as feedback, and it’s one of the largest uncertainties in climate modeling.

The big advance of Manabe and Wetherald’s work was to model not just the feedbacks but the interrelationships between the different components that contribute to the Earth’s temperature. As the atmospheric contents change, so do both the absolute and relative humidity, which impacts cloud cover, water vapor content and cycling/convection of the atmosphere. What they found is that if you start with a stable initial state — roughly what Earth experienced for thousands of years prior to the start of the industrial revolution — you can tinker with one component (like CO2) and model how everything else evolves.