Before we throw a shade on hydroelectric power generation, let's do a bit of fact checking first.
Earth's energy balance is determined by radiation received from the sun (over a wide spectrum of frequencies) and dissipation through radiation, with the infrared component being the one of concern. Any differences between incoming and outgoing energy is absorbed by all mass on the planet (or provided by Earth's mass in case of a negative balance). The high specific heat capacity of water lets the oceans act as a giant buffer - but the same is true for any surface water. Without the oceans, the same amount of heat added to the planet would cause a greater rise in temperatures.
Earth's atmosphere inhibits the outflow of energy, which is a good thing in general. Without any greenhouse gases, Earth would be a rather chilly place to be. The rapid rise in greenhouse gas levels over the last two centuries has tilted the scale too much and that's why many of us feel the urgency to drastically reduce the output of greenhouse gases and ultimately even actively reduce the level of CO2 in the atmosphere.
TLDR;
- Every kWh of electricity produced without releasing more CO2 helps fighting climate change
- It makes no difference to the total energy balance if the sun heats a lake by 1° or the same amount of air by 4°.
I don't consider nuclear to be a viable alternative to solar, wind and water but the amount of waste heat is not a valid argument. 240W/m^2 or solar energy reach Earth's surface. A nuclear power plant of 2.4 GW electrical output generates 4.8 GW of waste heat, which is about as much as 20 km^2 of Earth's surface receives as input. A square of about 4.5 km in length / width.
The main issue with nuclear is the generated waste that radiates for several thousands of years.
en.wikipedia.org
gcos.wmo.int
energyeducation.ca