SPIEGEL: Mr. Gabriel, in light of the threat of a climate catastrophe, many argue that -- as long as fossil fuels like coal and natural gas continue to pollute the atmosphere with carbon dioxide and renewable energies have been insufficiently developed -- that we should continue to use nuclear energy. Would that not be a sensible path to follow?

Gabriel: Renewable energy sources are already an important part of Germany's energy supply today -- and their share is growing faster than forecast. In purely quantitative terms, they replace one nuclear power plant every year. Furthermore, we're not phasing out nuclear energy from one day to the next. It will continue to be used in Germany for the next 14 years; that decision has been made. The question over which opinions diverge is how to assess the risks associated with extending the lifespans of the nuclear power plants that are still online. Proponents of nuclear energy always act as if we were faced with a choice between the plague and cholera, a choice between the risks of nuclear energy and the dangers of the climate crisis. But as a politician, I don't want to choose between two diseases -- I want to find the path to good health.

Claassen: I feel the environment minister's choice of words is inappropriate. The comparison to a "choice between the plague and cholera" is exaggerated. This attention-grabbing comparison to a disease is unfair to those who have worked in nuclear power plants for decades and, in doing so, have made a considerable contribution to climate protection. Many people have invested their entire careers, their expertise, their life's work to that area. Of course we have to balance the residual risk of an accident in the area of nuclear energy and the climate-protecting effect of atomic power.

Gabriel: The issue is not about a residual risk. That expression makes the problem seem harmless. The issue is that of the gigantic danger of damage in the case of an accident. Forsmark (the Vattenfall-owned plant in Sweden) has just shown us what sorts of things can happen with long running times. The point is that the narrowly averted accident did not occur in Ukraine or Russia, but in a technologically advanced country like Sweden.

Claassen: Nuclear energy has been employed in a safe way for decades in Germany.

Gabriel: Of course everyone who works in this industry is firmly convinced that nuclear energy can be kept under control. But we have had many serious hazardous incidents in Germany too -- despite the fact that all technicians had previously said they could not occur.

SPIEGEL: As far as the people outside the nuclear power plants are concerned, their worries about safety are what dominates the issue in their minds. Are you, Mr. Claassen, seizing on the opportunity provided by the fear of a climate crisis in order to repress the fear of a meltdown?

Claassen: Of course people's worries need to be taken seriously. One has to seriously balance the residual risk of a nuclear accident -- whatever the correct quantification of that risk -- and the problem of climate change, which threatens the existence of all of humanity.

SPIEGEL: The safety risks also include the fact that it remains completely unclear where nuclear waste, which stays radioactive for as long as a million years, should be sent for final storage.

Gabriel: Since the 1970s, 130,000 barrels of nuclear waste have been buried in a so-called experimental final storage facility in the former salt pit of Asse, not far from where I live. When I went in there for the first time as a 17-year-old, I asked: If two of three adjacent salt pits have suffered floods, what makes you believe that no water will seep into the third salt pit, the one you're now packing nuclear waste into? We were given many lectures on why that can't happen. Twelve cubic meters (424 cubic feet) of water have been flowing in there every day since 1988. No one knows how that can be stopped.

SPIEGEL: Mr. Claassen, what kind of advantage does nuclear energy provide?

Claassen: In our country, nuclear energy helps prevent the emissions of 150 million tons of CO2 every year. Carbon dioxide emissions would be that much higher if, instead of nuclear power plants, coal-burning power plants with the same capacity had been built.

Gabriel: We are convinced that we can bring the dangers of climate change under control in a much better way using instruments other than the use of nuclear energy. With the share of renewable energy sources on the electricity market currently lower than 12 percent, we're already preventing (emissions of) about 100 million tons of CO2. Assuming a conservative estimate -- not an optimistic one -- it is realistic that we can achieve a situation, by 2020, in which renewable energy sources reach a share of at least 26 or 27 percent.

If we had invested even a fraction of the many billions that we have put into nuclear energy into research into renewable energy sources, then we would neither have a CO2 problem today, nor would we face the risk of radioactivity.

Claassen: It may be true that we would have made more progress in the area of renewable energy sources. But most renewable energy sources do not have the capacity to provide the base load.

SPIEGEL: "Base load" is the term for the output constantly required by the electricity grid.

Claassen: Without nuclear energy, we would have to cover the base load almost exclusively by means of fossil fuels, namely black coal and brown coal, meaning that we would have emitted more CO2 today, not less, even if it had proven possible to develop renewable energy source technologies more quickly. A study by the German Energy Agency (DENA) -- not a study by the energy industry, that is, but one by the center of competence for energy efficiency in Germany -- came to the following conclusion: When 37,000 megawatts of wind power capacity have been installed, that will make 6 percent of those fossil fuel or nuclear plant capacities that can provide the base load obsolete. So 2,300 conventional megawatt blocks of coal or nuclear energy could then be abandoned.

SPIEGEL: That's not even 2 percent of today's electricity capacity.

Claassen: Roughly estimated, you would need about 10,000 wind turbines to reproduce one large nuclear plant. That should be clear to everyone who also bears in mind the landscape and other issues.

Gabriel: Those kinds of horrific figures are used to try to scare people. The DENA study on the electricity grid recommends developing as many as 20,000 megawatts of capacity in the form of offshore facilities -- at a distance from the coast where they can't even be seen from an island. That requires expanding the grid by 850 kilometers (528 miles) of AC power lines. It's the energy providers, by the way, who are responsible for doing so. That would provide stability for the grid and increase the capacity to provide the base load.

Claassen: When it comes to renewable energy sources, we have the capacity to produce the base load in the case of biomass and large hydroelectric facilities, but not in the case of solar power, wind power and other sources. That's why we have to raise the question of how we will cover the base load in the foreseeable future, for as long as there are no other technological options available.

Gabriel: You're reducing the use of renewable energy sources to electricity production. But the base load argument isn't even valid there. With biogas, we can produce the base load, and by expanding offshore windpower off the coast of northern Germany we of course become considerably more independent from the problems of the wind power facilities we have on the land. You're also completely ignoring the uses of bio-energies when it comes to fuels. Nuclear energy does nothing at all for us in this area. This means that if we really want to do something for climate protection, we have to consider the complete spectrum of energy resources.

SPIEGEL: Would the expansion of nuclear energy even have an appreciable effect on global climate development?

Gabriel: That's the point: Worldwide, nuclear energy contributes only 6.5 percent to total primary energy use; when it comes to total final energy consumption, the figure is less than 3 percent. In Germany, we're behaving as if the issue of the climate were to be decided over nuclear energy.

Claassen: What's correct is that, (INCORRECT!!!) with regard to worldwide energy consumption, nuclear energy is of rather subordinate importance compared to fossil fuels. That's different in countries such as France or the United States, but of course it was that way in China or India. That's precisely why we have these climate problems -- because the base load has been covered largely by fossil fuels in these countries. If we had had a substantially higher proportion of nuclear energy in countries such as China, which have relied very strongly on coal, during the last 30 years, then climate change would not be at such an advanced stage.

Gabriel: If you want to replace 10 percent of worldwide energy consumption by nuclear energy, you would have to build 1,000 new nuclear power plants. Now that's a truly horrific scenario.

SPIEGEL: That's as much of a horror scenario as the 10,000 wind power facilities that Mr. Claassen refered to.

Gabriel: First of all, the figure is not correct. We're talking about 20,000 megawatts. That equates to 4,000 facilities far offshore. And secondly, you're acting as if wind power were the only renewable energy source. Now that's nonsense.

Claassen: I didn't speak of 20,000 megawatts of installed capacity, but of the real output of a large nuclear power plant. And I didn't at all pretend that wind power is the only renewable energy source. That's why we're calling for hydropower, geothermal energy, biomass energy and solar local heat.

Demand for energy will rise enormously during the coming decades because that's when billions of people will first get proper access to energy in the first place. Today, only about 2 billion people are provided with energy the way we are. More than 4 billion are still waiting to get proper access to energy in the first place. Add to that another 3 billion inhabitants of the Earth by 2050. Assuming that the present population of China remains stabile, and presuming today's best available combination of renewable and fossil energy, the best technologies available today with the greatest possible performance: Without the use of nuclear energy, we would have an additional 3,500 tons of CO2 every year in China alone, assuming that per capita electricity consumption there is the same as that of the old EU member states (the EU 15). India, Indonesia and Brazil are not even considered in this calculation. Nor is population growth. Three thousand five hundred tons of CO2 are about seven times as much as heavy industry and the energy industry emit together here in Germany.

Gabriel: Does that mean you're recommending to the Chinese that they build nuclear power plants exclusively?

Claassen: I didn't say "exclusively."

Gabriel: But considerably, in any case. All I can say to that is: Get well soon!

Claassen: Dear Mr. Gabriel, there is today no scientifically verified scenario for how the world's growing hunger for energy can be satisfied without nuclear energy and without a climate crisis resulting. The reality we live in - not what Mr Gabriel wishes for - is that China and India will invest massively in nuclear energy. The United States and England will also invest in nuclear energy again, and Finland is already doing so.

Gabriel: Of course there is massive pressure to invest in new nuclear power plants from the British government, for example, because the British have no more natural gas reserves, because they have ceased coal extraction and because they have nuclear facilities that are so old that they urgently need to be replaced.

Claassen: According to our figures, 62 nuclear energy plants are on order worldwide at present.

Gabriel: That includes many projects that have in part been pursued for more than 20 years. In fact, there are only about 30 feasible building applications besides the 435 nuclear energy plants that exist worldwide. Out of them, more than 250 reactors are so old they need to be replaced with new ones within the next 20 years - which means that, worldwide, we don't have a real nuclear energy boom at all.

SPIEGEL: But China and India are choosing nuclear power.

Gabriel: China wants to cover four percent of its electricity needs by nuclear energy by 2020, but it wants to cover 16 percent with renewable energy sources. India does not have faith in the uranium supplies lasting much longer. So India is deciding to venture directly into the field of plutonium-based fast breeder technology. That immediately prompted an international debate over the creation of fissile material that can also be used to build nuclear bombs. Now, India is a democracy, thank God. But imagine if that the message of Mr Claassen and others -- that nuclear energy is necessary for saving the climate -- were heard the world over. By doing so, we would spread the capacity to build nuclear weapons the world over in a very brief time. And we would not be able to prevent any crazy dictator on this planet from doing so. So I can only warn against broadcasting such messages across the world.

Claassen: I have not broadcast any message and I have not given any recommendation on how to act. What I did, dear Mr Gabriel, was describe a purely physical-chemical-mathematical state of affairs. I don't know; it seems like we're no longer allowed to describe reality.

Gabriel: You're apparently afraid of the consequences of your own message, because the logical conclusion to be drawn from your position is the massive expansion of nuclear power plants, and not just longer running times in Germany.

Claassen: Once again, what I said was that if China should one day reach our per capita level of electricity consumption, that will lead, under the given premises (that is, without the use of nuclear energy), to CO2 emissions increasing by 3,500 million tons per year. That's not a question of fear or of some message, but of facts. Now, you don't have to react so aggressively, just because you don't have an answer to this.

Gabriel: Of course we have an answer. The international negotiations on climate protection this year will have the goal of reducing CO2 emissions by 30 percent until the year 2020. Since the developing countries have higher emissions, the industrialized countries will have to reduce their CO2 emissions by considerably more than 30 percent.

Claassen: No one has explained to me yet how these goals can really be achieved without nuclear energy. The real plans for power plants in Germany are such that the greatest part of the gap arising in the provision of the base load is to be covered by means of fossil fuels. That's why we're calling for a modernization of the phasing out of nuclear energy, in order to make the phase-out sustainable. To us, modernization means running times extended by eight or 10 years, in order to open a time window for research and development, one in which a transition to renewable structures becomes possible - instead of overhastily cementing fossile structures for decades.

SPIEGEL: Energie Baden-Württemberg (EnBW) has requested that so-called residual electricity quantities be transfered from the newer nuclear energy plant Neckarwestheim II to the older plant Neckarwestheim I. That way, the running time of Neckarwestheim I, which would likely end in 2017 under the current arrangement, would be extended into the year 2017. As a trade off, the running time of Neckarwestheim II would be shortened and would also end in 2017.

Gabriel: In fact Mr. Claassen does not want to take the newer power plant off the grid sooner either. He just wants to make it through the next national elections in the hope that a new decision will then be taken.

SPIEGEL: The phasing out of nuclear energy was decided consensually, in June 2000, between the two members of the then governing coalition -- the Green Party and the Social Democrat Party (SPD) -- and it was confirmed by the so-called grand coalition (of conservative Chancellor Angela Merkel and her conservative Christian Democrats along with the left-leaning Social Democrats) in its coalition contract.

Gabriel: Now the same companies that signed off on that decision are saying: Okay, we're still in favor of the phase-out, but please, not so fast. If we give in to them, they'll be back in five or eight years to ask for more seconds. Because the truth is that the four energy providers are not concerned about the climate, but rather about the many hundreds of millions of euros they're earning thanks to amortized nuclear power plants. And they won't invest a single cent of that money in newer or more efficient power plants.

SPIEGEL: First, German energy provider RWE requested a running time extension for its nuclear reactor Biblis A, a request the Environment Ministry rejected in March. Then EnBW followed suit, and now Vattenfall wants to keep the nuclear power plant Brunsbüttel on the grid until 2011 - two years longer than agreed.

Claassen: The accusation that we are just using climate protection to justify ourselves is one we feel doesn't apply to us at all. We submitted a request for the transfer of 46.9 terawatt hours from the residual electricity quota precisely in the way intended by the law. After all, the law explicitly created the "from new to old" option. We provided reasons for the request that we believe are convincing. Incidentally, the point is not to make it past the next election. We formulated a request for the period until 2017, after all. And more than one election is scheduled for the time between now and then.

Gabriel: I don't want to discuss the request here, since we're assessing it according to the standards of the law. But I ask myself why EnBW shies away from the comparison in terms of safety. Of course our decision also depends on whether the requested residual electricity transfer would be detrimental to the level of safety -- that is, whether the old reactor, for which the request projects an extended running time, fulfils the same safety standards as the newer, technically more developed reactor, which is to be taken off the grid earlier than originally intended. But EnBW has rejected such a comparison of the safety levels of the two reactors. And so of course I'm asking myself why.

SPIEGEL: Why do you want take the newer nuclear reactor off the grid sooner, Mr Claassen?

Claassen: First, let me say something with regard to the safety level comparison: The law on nuclear energy makes no provision for such a comparison. And with regard to our request: We want to use the synergies involved in the operation of two neighboring reactor blocks for as long as possible.

That doesn't just increase the level of profitabililty, by the way, but also that of safety. Given maintenance, plant management, availability of resources and the transfer of know-how, the simultaneous operation of both blocks undoubtedly yields positive synergy effects.

Gabriel: We believe that's not the true motive. Instead it is a trick the energy industry is trying to pull.

Claassen: It's no trick. We have to keep two things apart. One is the law and our requests as they are formulated within the framework of the law.

The other is the political opinion-formation and decision-making process that we take to be necessary. Independently of our request, let me state clearly that I am indeed of the opinion that the CO2 target values cannot be achieved on the basis of the schedule for phasing out nuclear energy in place today. I am indeed of the opinion that, if we implement the phasing out of nuclear energy according to the scheduled dates currently in place, we will destroy economic assets prematurely and overhastily. I am indeed of the opinion that we thereby unnecessarily fix in place fossil fuel structures. I am indeed of the opinion that we need to change the law.

SPIEGEL: What will happen if your request, Mr. Claassen, is not approved and Neckarwestheim I has to be taken of the grid in 2009?

Claassen: In that case, we would of course have to compensate. It is precisely for that purpose that a black coal-fired power station is being built in Karlsruhe. We had two energy carriers to choose from, black coal and natural gas. As far as gas is concerned, at the moment you can't get long-term delivery contracts with economically reasonable conditions. So only black coal remained as an energy carrier for producing the base load in this area.

Gabriel: Why don't you do something else in Karlsruhe? Natural gas isn't the choice available to you. Why don't you opt for intelligent technology like a cogeneration plant for heat and power? Constantly saying it has to be black coal attests to a lack of creativity.

Claassen: We don't need to be ashamed in front of anyone when it comes to creativity. We're investing in a compressed air storage plant in (the German state of) Lower Saxony, for example, that will make renewable energy production capable of producing the base load. In Rheinfelden, we're investing far more than €300 million ($405 million) in the largest renewable energy production project anywhere in Germany. We're building the first German wave farm, integrated into a coast protection measure on the North Sea. We're at the vanguard in Germany when it comes to geothermal power. We have said very clearly that we will support every biomass project in Baden-Württemberg that is economically viable and desired by the people in the area. I believe there is probably no other large German energy provider that is working as broadly and as deeply on the issue of renewable energy sources.

Gabriel: That shows that nuclear energy will not be the desisive factor in climate policy.

Claassen: Nuclear energy is not the solution to the climate problem -- that's entirely clear. But it is, for the time being, one part of the solution. We both want less CO2. The only issue we're arguing over is how nuclear energy should be addressed during an eight to 10 year period in Germany.

SPIEGEL: Why don't you both dare to make a prediction: When will the last nuclear power plant be taken off the grid in Germany?

Gabriel: 2020-2021.

Claassen: Sometime during the period between 2020 and 2030. Since I know how quickly the Environmental Minister is capable of learning, I'm confident that in the end he will himself contribute to ensuring that the date is closer to 2030 than to 2020.

SPIEGEL: Mr. Claassen and Mr. Gabriel, we thank you for this interview.