US voters will head to the polls tomorrow to decide which party rules Congress for the next two years. Environmental groups have spent millions trying to make climate change an electoral issue. Come Wednesday morning, they’ll see what those bucks bought.

The US legislature looks like it’s heading for a shake up. Polls show the Republican party has a good chance of winning a majority in both chambers of Congress for the first time in almost a decade.

That could have serious ramifications for the country’s climate policy.

US commentators have done a good job of rounding up what that could mean state-side. We take a more international perspective, looking at what it might mean for the world’s chances of agreeing a new global climate deal.

Midterms

Congress is a perennial thorn in the side of those pressuring the US to take action on climate change. The outcome of this week’s election could make the task a whole lot harder.

Unlike the President, who gets elected every four years, Congressional elections take place every two years. This week’s election is known as the midterms, as it’s held midway through the President’s term.

Every member of the House of Representatives and one third of the Senate is up for election. It’s of particular interest because the Republicans look likely to win a majority in the Senate for the first time since 2005. To do that, they need to win at least six extra seats – either by winning six and losing none or, more likely, winning more than that and not losing many.

It’s significant, because the Senate has a lot of important powers.

The Republicans need a two-thirds majority in the Senate to be able to prevent the Democrats blocking any new laws. They won’t win that many. So overturning the steps Obama’s administration has taken to curb the US’s emissions in recent years by passing new legislation isn’t on the table.

But they can obstruct and alter climate policy in other ways. The Senate has the power to ratify the budget and any treaties the president signs. It has used such powers to block climate action in the past.

Here’s what’s at stake this time around.

Obama’s plan

Last year, President Obama announced his climate action plan. The centrepiece of the policy is a new regulation requiring power plants to cut emissions 30 per cent by 2030, known as the clean power plan.

The Republican’s current leader in the Senate, Kentucky senator Mitch McConnell, describes the policy as “a massive, big-government boondoggle“, and has pledged to try and overturn it. There are a number of ways the Republicans could set about this if they win a majority in the Senate.

Congress can override the president if the House of Representatives and Senate both pass joint-resolutions – a kind of formal statement – as thinktank the Centre for American Progress and blog Climate Progress point out.

The Republicans already control the House of Representatives and look set to expand their majority this week. If the party gains control of the Senate as well, the Democrats would not have enough members of Congress to block such a move.

The Republicans could also add clauses to any legislation the Democrats and president really want passed, known as riders, with the aim curbing Obama’s plan.

If Obama’s clean power plan is rolled back, it could have serious implications for international climate negotiations. Lots of countries argue that they shouldn’t be expected to act until the US does as it has the world’s largest historical emissions. China’s approach to the climate negotiations has arguably softened since Obama announced his action plan.

If the climate plan was no longer in place, or significantly curbed, China and nations may be reluctant to commit to strong climate action. That would represent a big blow to negotiators’ chances of getting a new global climate deal in Paris.

Committee powers

If the Republicans gain control of the Senate, members of their party would also become chairs of some prominent committees. That would give a high-profile platform to some politicians vehemently opposed to tackling climate change, as The Nation points out.

Oklahoma senator James Inhofe would become chair of the Senate’s environment and public works committee. The committee has the ability to hold up, change, or scrap any climate change legislation. It also holds regular hearings on matters related to climate policy.

Inhofe describes climate change as a “hoax” and is strongly opposed to Obama’s clean power plan. He became known for aggressively questioning the validity of climate science in his previous tenure as the committee’s chair between 2003 and 2007.

If the Republican’s win, climate skeptic committee chairs such as Inhofe, Ted Cruz, and Ron Johnson could also move to cut funding to those charged with implementing Obama’s climate plan, such as the Environmental Protection Agency.

Combined, the committee chairs would make the Senate altogether less climate-friendly.

That could spook other governments in the run-up to next year’s international climate negotiations. If they don’t think the US’s more proactive approach to curbing emissions is going to last, they are less likely to agree to taking action themselves.

Global issues

The US’s efforts to curb emissions and the world’s prospects of taking action are largely synonymous.

Those unsure of the Senate’s international influence need only to think back to 1997, when a Republican Senate refused to ratify the Kyoto Protocol. That decision meant the world’s only binding agreement to cut emissions was hamstrung from the start. Many say it never recovered.

The Intergovernmental Panel on Climate Change yesterday spelled out the dangers of failing to tackle climate change in the clearest terms yet. How the US votes tomorrow will have a significant impact on the type of action the world agrees to next year.

That’s why environmental campaigners have spent millions promoting climate-friendly candidates. And it’s why it shouldn’t just be US citizens watching closely when the polls close.