(Bloomberg) -- The Swiss National Bank’s carbon footprint is far higher than reported because the central bank ignores indirect emissions from companies in its stock portfolio, according to a climate watchdog group.

The Climate Alliance estimates that such emissions are about four times as much as officials claimed last month. While the SNB said the firms it holds in its vast balance sheet generated 10.2 million tons of CO2, the group’s own calculations put the carbon footprint at as high as 41.7 million tons.

The SNB left out so-called “Scope 3” emissions that attempt to gauge the overall climate footprint of an organization’s supply chain, because “data for the companies in the portfolio is limited and the data quality is still insufficient,” according to the central bank’s sustainability report. “Data are based on estimates by third-party providers or voluntary and only partially verified information from the companies themselves.” 

The central bank didn’t respond to a request for comment on Monday, which is a public holiday in Zurich.  

Read More: SNB Discloses Carbon Footprint, Won’t Change Investment Policy

While “both the limited availability of data and its quality are a reality,” Climate Alliance says that “simply ignoring the corresponding emissions is unacceptable,” especially in light of the SNB’s investment approach of passive management of broad market indexes of industrialized and emerging countries.

In its sustainability report, the SNB also rebuffed calls to take a more active stance on climate change, saying it won’t alter how it deploys its foreign-currency reserves because it is not allowed to “influence economic, political or social developments through its investment policy.”

Last week, the European Court of Human Rights said in a landmark ruling that Switzerland had failed to protect its citizens from the ravages of climate change. 

The Swiss parliament is set to decide on Monday on a series of initiatives that attempt to force the SNB to take climate change into account in its monetary policy, saying it creates significant financial risks that could endanger price stability.

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