This year's Nobel Prize season approaches as Russia's invasion of Ukraine has shattered decades of almost uninterrupted peace in Europe and raised the risks of a nuclear disaster.

The secretive Nobel committees never hint who will win the prizes in medicine, physics, chemistry, literature, economics or peace. It's anyone's guess who might win the awards being announced starting Monday.

Yet there's no lack of urgent causes deserving the attention that comes with winning the world's most prestigious prize: Wars in Ukraine and Ethiopia, disruptions to supplies of energy and food, rising inequality, the climate crisis, the ongoing fallout from the COVID-19 pandemic.

The science prizes reward complex achievements beyond the understanding of most. But the recipients of the prizes in peace and literature are often known by a global audience and the choices — or perceived omissions — have sometimes stirred emotional reactions.

Members of the European Parliament have called for Ukrainian President Volodymyr Zelenskyy and the people of Ukraine to be recognized this year by the Nobel Peace Prize committee for their resistance to the Russian invasion.

While that desire is understandable, that choice is unlikely because the Nobel committee has a history of honoring figures who end conflicts, not wartime leaders, said Dan Smith, director of the Stockholm International Peace Research Institute.

Smith believes more likely peace prize candidates would be those fighting climate change or the International Atomic Energy Agency, a past recipient. Honoring the IAEA again would recognize its efforts to prevent a radioactive catastrophe at the Russian-occupied Zaporizhzhia nuclear power plant at the heart of fighting in Ukraine, and its work in fighting nuclear proliferation, Smith said.

“This is really difficult period in world history and there is not a lot of peace being made,” he said.

Promoting peace isn't always rewarded with a Nobel. India's Mohandas Gandhi, a prominent symbol of non-violence, was never so honored.

In some cases, the winners have not lived out the values enshrined in the peace prize.

Just this week the Vatican acknowledged imposing disciplinary sanctions on Nobel Peace Prize-winning Bishop Carlos Ximenes Belo following allegations he sexually abused boys in East Timor in the 1990s.

Ethiopian Prime Minister Abiy Ahmed won in 2019 for making peace with neighboring Eritrea. A year later a largely ethnic conflict erupted in the country's Tigray region. Some accuse Abiy of stoking the tensions, which have resulted in widespread atrocities. Critics have called for his Nobel to be revoked and the Nobel committee has issued a rare admonition to him.

The Myanmar activist Aung San Suu Kyi won in 1991 for her opposition to military rule but decades later has been viewed as failing to oppose atrocities committed against the mostly Muslim Rohingya minority.

In some years, no peace prize has been awarded. It paused them during World War I, except to honor the International Committee of the Red Cross in 1917. It didn't hand out any from 1939 to 1943 due to World War II. In 1948, the year Gandhi died, the Norwegian Nobel Committee made no award, citing a lack of a suitable living candidate.

The peace prize also does not always confer protection.

Last year journalists Maria Ressa of the Philippines and Dmitry Muratov of Russia were awarded “for their courageous fight for freedom of expression” in the face of authoritarian governments.

Following the invasion of Ukraine, the Kremlin has cracked down even harder on independent media, including Muratov's Novaya Gazeta, Russia’s most renowned independent newspaper. Muratov himself was attacked on a Russian train by an assailant who poured red paint over him, injuring his eyes.

The Philippines government this year ordered the shutdown of Ressa’s news organization, Rappler.

The literature prize, meanwhile, has been notoriously unpredictable.

Few had bet on last year’s winner, Zanzibar-born, U.K.-based writer Abdulrazak Gurnah, whose books explore the personal and societal impacts of colonialism and migration.

Gurnah was only the sixth Nobel literature laureate born in Africa, and the prize has long faced criticism that it is too focused on European and North American writers. It is also male-dominated, with just 16 women among its 118 laureates.

A clear contender is Salman Rushdie, the India-born writer and free-speech advocate who spent years in hiding after Iran’s clerical rulers called for his death over his 1988 novel “The Satanic Verses.” Rushdie, 75, was stabbed and seriously injured in August at a festival in New York state.

The list of possible winners includes literary giants from around the world: Kenyan writer Ngugi Wa Thiong’o, Japan’s Haruki Murakami, Norway’s Jon Fosse, Antigua-born Jamaica Kincaid and France’s Annie Ernaux.

The prizes to Gurnah in 2021 and U.S. poet Louise Glück in 2020 have helped the literature prize move on from years of controversy and scandal.

In 2018, the award was postponed after sex abuse allegations rocked the Swedish Academy, which names the Nobel literature committee, and sparked an exodus of members. The academy revamped itself but faced more criticism for giving the 2019 literature award to Austria’s Peter Handke, who has been called an apologist for Serbian war crimes.

Some scientists hope the award for physiology or medicine honors colleagues instrumental in the development of the mRNA technology that went into COVID-19 vaccines, which saved millions of lives across the world.

“When we think of Nobel prizes, we think of things that are paradigm shifting, and in a way I see mRNA vaccines and their success with COVID-19 as a turning point for us,” said Deborah Fuller, a microbiology professor at the University of Washington.

Physics at times can seem arcane and difficult for the public to understand. But the last three years, the physics Nobel has honored more accessible topics: Climate change computer models, black holes and planets outside our solar system.

Some harder-to-understand topics in physics — like stopping light, quantum physics and carbon nanotubes — could capture a Nobel award this year.

The Nobel announcements kick off Monday with the prize in physiology or medicine, followed by physics on Tuesday, chemistry on Wednesday and literature on Thursday. The 2022 Nobel Peace Prize will be announced on Oct. 7 and the economics award on Oct. 10.

The prizes carry a cash award of 10 million Swedish kronor (nearly $900,000) and will be handed out on Dec. 10.

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Jan M. Olsen in Copenhagen, Denmark, Jill Lawless in London, Laura Ungar in Louisville, Kentucky, and Seth Borenstein in Washington contributed.

The 2021 Nobel Prize in physiology and medicine has been awarded to David Julius and Ardem Patapoutian for their discoveries of receptors for temperature and touch.

The two U.S.-based scientists received the accolade for describing the mechanics of how humans perceive hot, cold, touch and pressure through nerve impulses.

Julius is a professor at the University of California, San Francisco. Patapoutian is a professor at the Howard Hughes Medical Institute at Scripps Research in La Jolla, California.

"Our ability to sense heat, cold and touch is essential for survival and underpins our interaction with the world around us," the Nobel Assembly said in a statement announcing the prize.

The discoveries will be vital to the development of treatments for chronic pain and other conditions, said Professor David Paterson, president of The Physiological Society in the United Kingdom.

"How we sense the temperature, touch and movement are some of the great questions for humanity," Paterson said.

Thomas Perlmann, the secretary general of the Nobel Assembly, said the discovery "unlocks the secrets of nature ... It explains at a molecular level how these stimuli are converted into nerve signals. It's an important and profound discovery."

Chili pepper

The starting point for the pair's groundbreaking discoveries was Julius' work with the humble chili pepper — or more specifically, capsaicin, the pungent compound that causes a burning sensation when we eat the peppers.

"It was a very clever thing to do because chili pepper, or capsaicin in the pepper, was known to trigger nerves or pain. David Julius thought it could lead to a breakthrough if we really understood the molecular mechanisms for how this occurs," Perlmann explained to CNN.

Julius and his team created a library of millions of DNA fragments corresponding to genes that are expressed in the sensory neurons which can react to pain, heat and touch. They then plugged genes from this collection into cells that do not normally react to capsaicin to find the single gene that caused the sensitivity.

Julius later realized this capsaicin receptor they discovered is also a heat-sensing receptor that is activated at temperatures that are perceived as painful, the Nobel Committee said.

"That was the route into these discoveries — the sensing mechanism for how nerves can actually be activated. When we encounter stimuli — temperature, mechanical, touch and pressure. The chili pepper was the handle but the discovery was much more profound than that," Perlmann said.

Patapoutian's work led to the discovery of sensors in the skin and internal organs that respond to "mechanical stimuli" that are felt as touch and pressure.

With his colleagues, he identified a cell line that reacted when its individual cells were poked with a micropipette. The team then identified 72 candidate genes that could be encoding receptors and "switched them off" one by one to discover the one responsible for mechanosensitivity.

Abdel El Manira, an adjunct member of the Nobel Committee for Physiology and Medicine, said the discoveries were made more than a decade ago but were particularly poignant given the coronavirus pandemic.

"It's the right time (for it) to be recognized. It profoundly changed our view of how we sense the world ... In the last year, we have missed our sense of touch — during a hug for example. These are the receptors that give us the feeling of warmth and closeness," he said.

'Holy grail'

Mike Caterina, the Solomon H. Snyder professor of neurosurgery at John Hopkins School of Medicine, worked with Julius in his lab as a postdoctoral researcher in the mid-1990s when the first discoveries about capsaicin in chili peppers were made.

"It had been a holy grail in the pain field. People knew that this receptor existed but there was no molecular handle," Caterina said.

"The sensation that we get when we eat spicy food is something so familiar and it has such a personal and cultural significance to so many people and everyone has a hot food story and everyone has experienced painful heat.

"So for those two very tangible experiences to be explainable with one molecule is what really made that work exciting to us."