According to The Global Shaper Survey  conducted by World Economic Forum, top three problems of today’s world are: 1) Climate change / destruction of nature 2) Large scale conflict / war and 3) Inequality. These problems are not created by wrong doings of only a class of people or of particular nation. Rather they are caused by contribution of all individuals of the world.
All world’s problems are robustly interconnected and have single root cause i.e. consumerism based life style of people, which is why single solution will work for them all. That single solution is Spiritual living.
Spiritual living is based on understanding and realization that we are not just body but soul. And soul is part and parcel of supreme soul, under whose direction the whole cosmos is working. Spiritual living means life is lived not just for satisfaction of mind or body but for that of soul, according to laws given by supreme soul. One cannot live happily by giving any amount of comfort to mind and body, unless he gives comfort to soul. When we work for the satisfaction of soul in connection to supreme soul, our mind and body will automatically be happy and satisfied. This is confirmed in Bhagavad Gita, the most authenticate book on Spiritual living.  Practical guidelines for spiritual living is explained below along with its contribution to solving world problems:
1) Climate change / destruction of nature:
This century old problem is the result of excess emissions of greenhouse gases into the earth's atmosphere, mainly from excessive “Industrialization.” Direct cause for this is 'turbo-consumerism', of people responding to 'hard-sell' marketing and acquiring repeatedly what they want, rather than what they need.  In the pursuit of pleasure for body man is working hard creating artificial things which mankind really don’t need. And by turning toward unnatural diet we have created artificial arrangement to produce food i.e. slaughterhouse industry, which is number one contributor to the destruction of nature .
The very first principle of spiritual living, simple living high thinking, solves this problem. Simple living is explained in Srimad Bhagavatam (scientific book on spiritual living) and other Vedic literatures as life dependent more on nature, the arrangement of Supreme. World renowned scholar His Divine Grace A.C. Bhaktivedanta Swami Prabhupada explains in his commentary on Srimad Bhagavatam that only little energy is required to develop and run a civilization based on agriculture and cow products. Such civilization will provide man with enough stock of food, clothing and shelter for healthy and happy living. It also guarantees full employment from decentralized economy stressing cottage industries and hand craftsmanship. A spiritual society utilizes certain modern advancements like electricity and printing, but because the general population returns to a materially simple life, the amount of industry retained presents no environmental problems. More of man’s energy can be utilized in developing the spiritual understanding, to solve the real problems of life: birth, death, old age and diseases.
So called educated man may disregard this as primitive living but all his advancement is turning him back to nature dependent living only. We replaced earthen vessels with steel and plastic vessels to again return to the same for health benefits . We replaced cotton cloths with terylene and terycot to return to the same in wake of skin protection . We produced processed food replacing natural food to keep up with fast life and turned back again in the search of health benefits. The list of such failed advancement and turning back is very long, ending with our cry for again growing forests to save earth from becoming an oven.
Thus spiritual living is all perfect solution for the number one problem of today’s world, climate change.
2) Large scale conflict / war:
No conflict or war happens for single reason. Among many factors for war, top three are 1) Economic gain 2) Territorial gain and 3) Religion . According to the Encyclopedia of Wars, out of all 1,763 known/recorded historical conflicts 93% had either economic gain or territorial gain as primary cause. .
Root cause for all conflicts, be it individual, communal, social, national or international, is one i.e. self-centeredness. When man identifies himself as body and only those related to his body as his kinsman, he acts in way which conflicts with the interests of others.
All the authenticate scriptures of world states that we are not body but spirit soul, part and parcel of Supreme soul, and so are all living entities. Constitutional nature of spirit soul is to render service therefor we are always rendering service to someone, either to our family, friends, community, society or nation. If we have no one to serve, sometimes we keep a pet cat or dog and render service to it. In spite of serving to the best of our ability, we end up being in conflicts at individual, communal, social or national level. This is because the service being rendered is not properly directed. For example, if we want to render service to a tree, we must water the root. If we pour water on the leaves, branches, and twigs, there is little benefit. If the Supreme soul is served, all other parts and parcels will be automatically satisfied. Consequently the end of self-centeredness as well as conflict-free service to family, friends, community, society and nation are realized by serving the Supreme Personality of Godhead. Therefor if populace of the world is educated with this spiritual science and trained to serve Supreme soul then there will be no conflicts.
The Cambridge dictionary describes inequality as “the unfair situation in society when some people have more opportunities, etc. than other people”. The United Nations describes it even more simply as “the state of not being equal, especially in status, rights and opportunities”. While the term itself is quite vast and has various interpretations, for the purpose of simplicity, the two large umbrellas under which we can classify inequality would be economic inequality and social inequality. Both these categories are deeply intertwined and inequality in one often affects the inequality in another. 
Economic inequalities are caused by over industrialization. And it can be solved by implementing spiritual civilization, described above, which brings decentralized economy for upliftment of all people. Social inequalities are caused by people’s identifying themselves with body belonging to particular gender or class. When human beings are educated with spiritual knowledge, as explained above, to see everyone as part and parcel of Supreme soul they will naturally regard all living entities, including other species, as equal and important. In this way there will remain no inequality of any sort.
Thus adding spiritual science in education system and providing training to people to implement the spiritual living will solve world’s biggest problems.