Cruising_World_2016-06-07

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by

Courtesy of Hunter Marine

century. That shift determines

where the maximum precipi-

tation falls, where it rains on

land, and how cyclones get

steered over water. If you’re a

farmer in Africa or a fi sherman

in the Atlantic, or sailing in

those areas, that’s going to be a

very big deal.

PV: Some of the changes in

the climate models seem

counterintuitive, such as

diminished wind speeds

in tropical and sub tropical

zones and an increase in

trade winds. What causes

that?

Rasch: When we talk about

climate, as opposed to weather,

we have to think about how

the wind fi elds and ocean cur-

rents distribute heat around

the planet. More energy tends

to get soaked up in the equa-

torial regions, and that heat

gets redistributed to the rest of

the planet by wind and ocean

currents. The polar regions

radiate some of that heat back

into space. Winds carry equa-

torial heat to the poles, along

with greenhouse gases, in great

circulation patterns that have

been controlling our global cli-

mate for centuries.

We’ve detected a spin-

ning down of those circula-

tion patterns, a diminishing of

winds associated with those

patterns, in the tropics. Some

circulations go north and

south while others go east and

west. These circulation pat-

terns, and percolation systems

in the ocean, deep under-

water, move heat around the

planet. Right now, all of those

patterns of heat distribution

are in a state of fl ux.

PV: What do climate models

tell us about the infl uence of

El Niño and La Niña events

in coming years?

Rasch: The models predict

that these patterns are going

to intensify. There’s also a

suggestion that the El Niño

southern oscillation pat-

terns are shifting eastward.

Rising ocean temperatures

will change El Niño’s inten-

sity and position, and this

will have far-reaching con-

sequences, a kind of cascade

of eff ects. The coastlines of

Peru and Chile, for example,

enjoy an upwelling of nutri-

ents from deep in the ocean

that brings food to their fi sh-

eries. Small changes in those

currents and ocean temps can

have big impacts downstream.

Fisheries scientists in the

Southern Hemisphere are very

worried about this because it

has the potential to aff ect huge

population centers in South

America and Africa.

PV: You’ve said that sailors

tend to think of weather

patterns over water, when in

fact many of those patterns

are set in motion by phe-

nomena on land. Could you

tell us a bit more about that,

and how climate change will

infl uence those patterns?

Rasch: A good example of this

begins in Africa. There’s been

a shift in rainfall patterns over

Africa that’s associated with

GREEN WAKES

This map from August 2015 shows sea-surface temperature

anomalies. The dark red is 5 degrees C above average.

COURTESY OF NOAA