There are two ways that the rise in sea level can affect people on the ground.
One is low-lying areas where the surface is very close to sea level.
There's a gradient in the water in the
soil, between fresh water that comes from rainfall that
can be used to feed the crops,
versus salty water that's encroaching from the ocean.
If you raise the sea level and you bring this
salty water too close to the surface, you can poison the agriculture.
There are islands in the Pacific,
low-lying islands that are making plans to evacuate in the coming years,
because their agriculture is no longer possible, because of salt encroachment.
But a more dramatic impact of sea-level rise comes during
storms which tend to pull the sea level up.
It's called a storm surge.
It's like a really high tide that follows a hurricane.
Hurricane Sandy, for example, in New York, had sea level
higher than it would have, if global sea level hadn't been rising
over the last few decades.
What's important is when the
sea level crosses some critical height, where suddenly
it can spill over a levee, or flood the subways, or something like that.
The rise in the background sea level coupled with storms
that seem to be increasing in their severity, which we'll talk about next,
can multiply each other, to exacerbate
the impact of rising sea level.