Voters in Berlin will go to the polls this weekend to decide on a proposal that would force the city government to drastically ramp up the German capital’s climate goals.

Sunday’s referendum, which has attracted considerable financial support from US-based philanthropists, calls for Berlin to become climate neutral by 2030, meaning that within less than eight years the city would not be allowed to contribute further to global warming.

An existing law sets the deadline for achieving that goal at 2045, which is also Germany’s national target.

The centre-right Christian Democratic Union, which won a recent local election in the capital and is likely to lead its new government, opposes the earlier target but would be bound to implement it if the referendum passes.

Jessamine Davis, a spokesperson for the grassroots group that initiated the vote, said Berlin’s current target is not in line with the 2015 Paris climate accord, which aims to cap global warming at 1.5C compared with the pre-industrial average.

“This is a very ambitious target, we’re clear about that. And it won’t be easy,” she said of the plan to cut almost all emissions by 2030. “But the climate crisis is an even bigger challenge.”

Ms Davis pointed to the flooding disaster in western Germany two years ago that killed more than 180 people and caused tens of billions of euros in economic damage.

Scientists say such disasters could become more likely as the planet warms. By contrast, redesigning Berlin’s city-wide heating network so it becomes carbon neutral is estimated to cost four billion euros, she said.

Polls show Berliners are narrowly in favour of the proposal, but the law also requires that it win the support of at least 25% of the city’s 2.4 million eligible voters to pass — something that could be harder to achieve on a day when no elections or other votes are taking place.

To draw attention to the referendum, Ms Davis’ group has conducted a large-scale advertising campaign, helped by donations of almost 1.2 million euros. While about 150,000 euros came from crowdfunding, most of the money was provided by philanthropic organisations and individuals.

A poster regarding the referendum in Berlin
A poster regarding the referendum in Berlin (Markus Schreiber/AP)

The biggest chunk – more than 400,000 euros – came from German-American investors Albert Wenger and Susan Danziger.

In emails to the Associated Press, Mr Wenger said the US-based couple had “a long history of supporting climate movements and making investments in innovative solutions to the climate crisis”.

“The Berlin ballot initiative demonstrates that citizens in a democratic process are demanding faster and stronger climate action,” he said. “This is a replicable model for the rest of the world and could result in achieving climate neutrality by 2030 before major tipping points are crossed.”

Stefan Evers, a senior politician with the Christian Democrats, said his party acknowledges the “historic challenge” of climate change and the impacts it is already having on Berlin and its 3.7 million inhabitants.

The party has proposed increasing the budget for climate-related measures by five to 10 billion euros, but Mr Evers said the investments required if the referendum passes would break the bank.

“Everybody who votes ‘yes’ on Sunday needs to ask themselves: Do we want to make drastic savings on kindergartens, schools, public sports facilities, homeless aid and social housing because of this referendum, or not,” he told fellow politicians on Thursday.

Mr Evers warned that if estimates of a 100 billion-euro price tag for the measures are accurate “then in a few years Berlin won’t be climate-neutral but bankrupt”.