First of all, these greenhouse gas emissions trap more heat in the atmosphere, increasing the temperature around the world. This is clearly visible on this first graph from NASA, wich shows the yearly deviation of temperature relative to the 30 year average of 1950-1980. On the second video you can see what u2018average temperatureu2019 means, in other words this is an average increase, considering all places in the world, so some of them will increase the temperature, some will decrease, but the on average the worldu2019s temperature will increase. Also, there is some yearly variation, this increase isnu2019t always forward, there are hotter years followed by colder years, but you can clearly see the tendency to an increase in temperature.
The increase in temperatures causes ice to melt, both glaciers (ice over land) , like Greenland and Antarctica and on the mountains all over the world, and icebergs (ice floating in the sea) such as the big ones in the Arctic Ocean. These graphs show a clear tendency of ice cover decrease in both glaciers and icebergs. Loss of glaciers causes sea level rise and affects coastal populations. Loss of ice on mountain glaciers cause a decrease in water resources for populations living in those areas. Iceberg melt doesnu2019t cause sea level rise, think of an ice cube on a glass of water, however it can cause changes on the ocean currents and furthermore, it decreases reflection from sunlight, which in turn increases temperature. This is a dangerous positive feedback loop on the climate, which means that the effect of temperature increase, ice melt, increases its cause, the temperature itself, keeping a circle of ever increasing temperature which can lead to the disappearance of the glacier.
Sea level rises as consequence of land ice melt, as explained above, but as a consequence as well of the thermal expansion of the oceans. There are some other factors but these are the main ones, and contribute approximately the same to sea level rise. Sea level rise can cause more extreme events on coastal areas and ultimately the disappearance of islands and the displacement of coastal populations.