Germany's federal government significantly downgraded its official forecast for national gross domestic product (GDP) growth in response to renewed uncertainty over the prospects of the global economy.

According to latest autumn forecast published on Thursday by the Economy Ministry, German GDP will expand by 1.8 percent in both 2018 and 2019, sharply down from the previous prediction of 2.3 percent and 2.1 percent, respectively.

The ministry cited expectations of weaker international trade, and hence only "relatively modest" gains for German exports, as the principal reason for the gloomier outlook. "Uncertainty about the further development is caused by increasing protectionist tendencies and international conflicts over trade," economy minister Peter Altmaier said.

At the same time, the CDU politician emphasized that Germany was still experiencing a phase of growth and would "already enter the tenth year of expansion" in 2019. "This is the longest growth phase since 1966 and the second-longest of all time," Altmaier added.

The federal government's autumn forecast forms the basis for more detailed estimates of prospective tax revenue and budgetary means at the disposal of federal, state and municipal authorities, as well as the German public health insurance scheme. The ministry for the economy traditionally follows the prior recommendations of five leading research institutes, which produce a bi-annual "joint prognosis" together, in its own calculations of future growth.

Although inflation is anticipated to rise from currently 1.8 percent to an annual average of 2.0 percent in 2019, the five institutes are currently confident that household spending power in Germany will remain strong thanks to rising wages. They further estimate that the government will record a massive budget surplus of 54 billion euros (62.5 billion U.S. dollars) in 2018 which will subsequently decline to 41 billion euros by 2020 as a consequence of more expansive fiscal policy.