Germany's plans to close all of its nuclear plants by 2022 will add up to 40m metric tons of CO2 emissions, analysts say.
Extra carbon emissions will come from the country's increasing reliance on fossil fuels, increasing demand for carbon permits under the EU's trading scheme.
"We will see a pick-up in German coal burn," said Barclays Capital analyst Amrita Sen.
"Longer term, they will be using more renewables and gas but this year and next, we should see a lot of support for coal burn."
Analysts have warned that as Germany uses carbon-emitting gas and coal to plug a power generation gap, the resultant increase in greenhouse gases would be equivalent to the annual emissions of Slovakia.
The phase-out has been criticised as a political move as German Chancellor Angela Merkel tries to capture anti-nuclear sentiment in the aftermath of Japan's Fukushima crisis.
Environmentalists welcomed the shift and hoped it would spur a shift to renewable energy such as wind and solar power, viewed as less harmful by avoiding radioactive waste.
Deutsche Bank analysts estimated an extra 370 million metric tons of carbon dioxide emissions through 2020, compared with Societe Generale's extra 406 million metric tons.
Matteo Mazzoni, analyst at Italy's Nomisma Energia, estimated an extra 20-29 million extra metric tons of CO2 per year.
"This is not likely to drive prices much higher in the medium term, unless the price of power comes under pressure," he said, referring to the price of emissions permits called EU allowances (EUAs).
"Carbon prices should obviously also get an uplift due to the sentiment born from the decision, but it will be limited and temporary," Socgen analyst Emmanuel Fages said.
"The market remains largely oversupplied EUAs for two years to come, capping any significant price increase in the short run."
The EU trading scheme is meant to limit industrial emissions by allocating a fixed quota of EUAs to some 12,600 factories and power plants but recession in 2009 left a glut of permits.