A ranking of 18 leading Irish or Irish-based firms compiled for the Sunday Tribune by London-based environmental research organisation Trucost found that Ryanair is Ireland's biggest greenhouse gas emitter in terms of emissions per 1m of turnover.

The company was followed by luxury goods manufacturer Waterford Wedgwood and construction materials firm CRH. Ryanair's Irish rival Aer Lingus wasn't included on the list because it had only recently been floated and data was not yet available.

Although the airline tops the list, according to Trucost head of environmental finance Neil McIndoe, Ryanair is far more efficient in some ways than its European competitors.

"The company is interesting because they are very carbon dioxide-efficient when ranked by passenger kilometre.

They have new planes and they fly them full. Because of their low-cost business model, their turnover is comparably lower than other airlines when measured against passenger numbers, which means they are bottom of their sub-sector on the MSCI world index of shares. In terms of emissions per kilometres though, they are one of the leaders, " he said.

McIndoe said that CRH, although highly ranked among Ireland's greenhouse gas emitters, performs very well compared to its peers.

"Of the eight construction materials firms we have looked at, CRH come in second-best in terms of emissions intensity, " he said, adding that the company was very good at reporting environmental data and used GRI, the global environmental reporting standard, in its reports, which are audited by independent consultants. "With regard to reporting, they are very firmly top of the class in Irish terms, " he said.

While the list contained few surprises, McIndoe said what was notable about the Irish list was how few companies were publishing environmental figures, with only three of the 18 publishing information and Trucost having to rely on its own estimates to assess the emissions of the remainder.

British firms are much farther ahead, with 16% publishing environmental data that was readily usable and another 26% publishing data that Trucost could use once it was clarified and elaborated upon by the company.

Trucost compiles emissions ratings on 3,200 companies worldwide and sells this data to the investment community. McIndoe said the three biggest consumers of this data at the moment were pension funds, investment managers and fund salespeople.

"A growing number of pension funds want to do a carbon footprint analysis on their holdings. That means drilling down through the data, assessing a company's emissions and scaling that to a fund's holding in the company, so they can assess just how many tonnes of emissions the fund is responsible for and then match that to benchmarks such as the FTSE All Share, " he explained.

Fund managers are meanwhile starting to realise that environmental impacts are beginning to be internalised on balance sheets through regulation and are waking up to the fact that emissions will begin to affect a share's value.

Consumer pressure matters far less the bottom-line implications.

"Finally, there are those on the sales side who want to launch green funds and need the data. We already have several on the market and I suspect we will see a lot more, " McIndoe said.

If fund managers are beginning to pay attention to this data, then canny chief executives should see which way the wind is blowing and start publishing their figures, he said.

"It isn't the most important thing affecting share price but it is becoming increasingly important.

What's more, it doesn't involve rocket science to get this information out, " he added.

In compiling its rankings, Trucost examined greenhouse gas emissions and factored in direct emissions and what are termed as first-tier indirect emissions. Direct emissions come from things such as industrial plants and airplane or vehicle fleets.

First-tier indirect emissions cover supplied electricity and, in the case of many businesses, these can be far higher than their direct emissions.

While it is possible to move further down the supply chain, the further you go, the harder it becomes to sort out who is responsible for emissions.

While some companies have made data publicly available, in the case of most Irish firms Trucost has had to come up with its own estimate. This is a two-step process. To calculate emissions, Trucost has identified 131 different industrial sectors and built up an environmental profile of the typical firm operating in this sector.

McIndoe said it was quite easy to build an accurate profile.

"There is fabulous data on this kind of thing because industrial processes are pretty well analysed and understood. So you go to something like the Toxic Release Industry database in the US and there is tremendously detailed information there, " he explained.

Each company is then mapped to these profiles and in many cases companies can cover several profiles.

Grafton Group, for example, covers sectors such as transport and logistics, warehousing and retail.

The next step is to send companies a verification sheet in which they are informed of Trucost's estimate of their environmental impact and given the right to respond. This can sometimes lead to productive dialogue, as in the case of Ryanair, when there was discussion on which methodology to employ to calculate the emissions generated from fuel use figures.

"It used to be the case that very few companies would offer a return. Occasionally an American company would offer to sue us if we published, or a German company would say they have far more data they would like to share with us. That situation has changed and a lot of the data we now get is from firms we have a relationship with.

Ryanair is one example and this is what we always hope will happen. We would always been keenest to take data directly for the company, " McIndoe said.

"However, you have to make sure the company isn't trying to pull a fast one or . . .and this is quite common . . .they make a mistake. We had one case recently when one firm more or less said they were responsible for two thirds of the world's carbon dioxide emissions. It turned out that they had got a decimal point wrong. Most financial directors would have no idea whether a figure is right or not when they are signing off, " he said.

The worst offenders

1DCC PLC
2 INDEPENDENT NEWS & MEDIA
3 PADDY POWER PLC
4 ALLIED IRISH BANKS PLC
5 DEPFA BANK PLC
6 ANGLO IRISH BANK CORP
7 BANK OF IRELAND
8 IRISH LIFE & PERMANENT PLC

Note: rankings are provided by UK-based carbon audit firm TruCost, based on estimated or disclosed carbon emissions per 1m of revenue