US climate change bill: thumbs up or down?

Democrats in the US Congress are expected to pass Barack Obama's climate change bill tomorrow. The bill aims to cut US emissions to 17 per cent below their 2005 level by 2020, with an 80 per cent reduction targeted for 2050. 

Writing in the Guardian, George Monbiot pointed out some serious flaws in the bill: 

The cut proposed by 2020 is just 17%, which means that most of the reduction will take place towards the end of the period. What this means is much greater cumulative emissions, which is the only measure that counts. Worse still, it is riddled with so many loopholes and concessions that the bill's measures might not offset the emissions from the paper it's printed on...

There are mind-boggling concessions to the biofuels industry, including a promise not to investigate its wider environmental impacts. There's a provision to allow industry to use 2bn tonnes of carbon offsets a year, which include highly unstable carbon sinks like crop residues left in the soil (another concession won by the powerful farm lobby). These offsets are so generous that if all of them are used, US industry will have to make no carbon cuts at all until 2026.

While environmentalists acknowledge the flaws in the bill, many say that it must be passed to provide a stepping stone for stricter cuts in future. Mobiot seems to agree: 

Even so, I would like to see the bill passed, as it at least provides a framework for future improvements. But why do we expect so little from the US? Why do we treat the world's most powerful and innovative nation as if it were a failed state, rejoicing at even the faintest suggestion of common sense?