Richard Grossman replied 25th Dec '13:
I am aware of two reasons that cities appear to sink. First is that that water is withdrawn from the porous ground underneath, causing sinkholes. The second is that ocean level is rising. I am not an expert on this field, since I live at 7000 feet altitude (about 2750 meters). In both cases the reason for the apparent sinking of land and the human disasters is overuse of resources.
Sinkholes are caused by the collapse of land after water has been removed by wells. In this case the resource that is overused is water--an essential resource for humans and all other living beings. The availability of water is the limiting factor for many areas, but especially in deserts. When the land's (or ocean's) carrying capacity is exceeded, disasters such as a die-off or sinkhole can result.
The situation is a bit more complicated with ocean rising. The immediate cause of ocean level change is the warming climate; warm water takes up more space than cold water. Climate change is caused primarily by our use of fossil fuels, which emit the greenhouse gas carbon dioxide (CO2). In the past there were enough plants (primarily trees) to absorb the low levels of CO2 that went into the atmosphere, but since the Industrial Revolution the volume of greenhouse gases has overwhelmed plants' ability to absorb them.
How can we prevent further problems with sinkholes and ocean level rise? The answer is not easy for either problem, but it is easier for sinkholes because they are localized.
It is possible to determine if the rock into which a well is drilled is likely to cause a sinkhole. If it is, water should not be withdrawn at a rate that is faster than it is replenished.
Ocean level rise and climate change are both global problems, because oceans cover so much of our globe and the atmosphere covers it all. We can slow the rate of climate change by decreasing our use of fossil fuels, employing more renewable energy. Another important factor is the number of people on the planet--fewer people would decrease greenhouse gas emissions. There are millions of people worldwide who don't have access to modern birth control. Thus, there are millions of unplanned pregnancies worldwide (including in rich countries). If all children born were planned and wanted, there would be less of a problem with the ocean rising.