Every energy source needs to be looked at with a cost-benefit analysis. The materials for wind and solar are not impact-free, and neither is their use. Before we condemn dams, we should compare them to alternative energy sources that would have been used instead (at the time of building), and assess whether the damage is less or more. Dams may be causing the extinction of a few species (which I assume implies they may yet be saved), but we can't assume that an increase in coal or nuclear power would be impact free in overall climate health or the health of individual species (nuclear has a fairly good track record by plant, but statistically having more plants built in the past may have yielded a disaster, and it only takes once to drastically change the averages for nuclear to significantly worse).

The question is, can new dams be built in ways that reduce or eliminate the problems we've encountered so far?

But the big difference is that the effects are almost completely local and not anywhere as threatening on a global scale compared to burning stuff and causing everything to heat up. This is actually a decisive point because whoever builds the dam will also lookout for the effects it causes and be more reasonable.

On top of that I think that the extinction of species is really not comparable to global warming, which will probably cause mass extinctions on a scale that has not been seen before in human history.

Actually, if mhurron is referring to what I think they are, then it can be fairly global. Think fish migration and spawning, such as with Salmon. Global Salmon population is very susceptible to being disrupted by blocking rivers. That said, I believe there are modern ways to address this problem.

Every dam worth a damn has fish ladders.

https://en.wikipedia.org/wiki/Fish_ladder

Poorly built dams can damage the environment. Except you know, its 2016 and we've figured out how to preserve the environment while providing clean energy now.

The wikipedia article links to this: http://e360.yale.edu/feature/blocked_migration_fish_ladders_...

Not exactly a glowing recommendation.

It seems a lot like those 'nature bridges' over highways that animals never use. A nice idea if it worked, but they don't.

Salmon, as an example, turn out to be a major component of nutrient transfer mechanisms returning fertilisers from sea environments to littoral watershed regions.

http://www.inforain.org/reports/salmon_decline.html

The obvious impact is local, but rivers have sweeping ecological importance, and we dam every one of them.

This is akin to saying that stepping on a nail is just as bad as walking into an industrial meat grinder, since they will both hurt your foot.

I don't think anyone is arguing that dams are zero impact. They can and do negatively impact local ecologies, and have the potential to impact animal populations at a broader scale. These problems can theoretically be offset to some degree with good planning and management, but thus far management has been uneven and middlingly successful.

I'm not being flippant and dismissing extinctions and the disruption of food chains as "breaking a few eggs": they are tragedies, but they are extremely small-scale tragedies compared to the ongoing disasters all other forms of reliable energy generation are inflicting on us. Hydro isn't above criticism, but blanket declarations that it's just as bad as fossil fuels is incredibly dangerous misinformation.

If your point of view is that any energy generation that in any way negatively impacts the environment are anathemas and that we should all be living in caves, then okay, but I don't know how you're powering your computer. Otherwise, you're being hyperbolic and enabling regressive and catastrophic ideas and practices.

A large part of the reasoning behind building many of the dams in the U.S. was flood control. In fact, I think the Hoover Dam was built for flood control reasons, and the hydroelectric part was the means to pay for it.

Enabling consistent river flows, which enables human settlement and farming in otherwise desert areas is definitely an environmental impact, but it's not clear that it is a bad impact.

And not burning fuel is certainly a positive in the eyes of global warming. All that fuel burning could result in rather permanent environmental changes of its own as sea levels rise, etc. If global warming is caused by CO2, then if we got all our power from dams instead of burning fuel, that seems like a place we'd like to get to right about now.