UN Finalizes Declaration on Sea Level Rise

UN Member States have fi nalized negotiations on a concise, action-oriented declaration addressing the growing threat of sea level rise.

The declaration is expected to be adopted by consensus at a UN General Assembly high-level plenary meeting on September 24, 2026.

The four-page declaration expresses deep concern over rising sea levels and calls for stronger international action, including implementation of international law and protection of the shared marine environment.

It identifi es four key areas for action: knowledge, data and science; adaptation, fi nance and resilience; livelihoods, socioeconomic challenges, culture and heritage; and the legal dimensions of sea level rise.

The declaration draws on scientifi c assessments by the IPCC and other international bodies and highlights the need for nature-based solutions and ecosystembased approaches.

It also notes the relevance of recent International Court of Justice and International Law Commission work on sea level rise and international law.

The UN held its fi rst highlevel meeting on sea level rise in September 2024.

Bangladesh Gas Supply Chain: Challenges and Prospect

Seven months into the new BNP-led government’s term, Bangladesh’s energy and power sector remains under severe strain.

The country has experienced unprecedented load shedding amid shortages of primary fuel, while its proven recoverable gas reserves continue to decline.

Efforts to discover major new resources may take time, and LNG imports remain constrained by inadequate infrastructure and high global prices.

The disruption of supply chains following the closure of the Strait of Hormuz has added another layer of uncertainty.

The new government has inherited an energy sector burdened by shortages, rising costs and heavy debt.

It has launched several initiatives to address the crisis, ranging from accelerated domestic gas exploration and LNG imports to connecting Bhola’s stranded gas resources to the national grid and pursuing offshore exploration.

This article critically examines these initiatives and considers what more may be required to put the sector on a sustainable path.

Drilling of 50 and 100 Wells The government has announced plans to revitalize the drilling initiatives of the previous regime after identifying key issues and challenges.

The activities of BAPEX, SGFL and BGFCL have been revitalized.

One of the major challenges identifi ed is the protracted DPP approval process, an essential nuisance.

It is alleged that DPPs often take more than a year from the conceptual stage to approval.

Unnecessary questions are also raised by inexperienced government offi cials.

The government must streamline the DPP approval process to expedite gas exploration and development initiatives, considering them toppriority national projects.

Land acquisition is also a critical activity for drilling projects.

The government must assist the executing agencies in shortening the process.

A drilling project requires land development and access-road construction before the drilling rig can be mobilized and work can commence.

Our EandP company, BAPEX, and production companies, BGFCL and SGFL, have achieved commendable success despite several constraints.

We expect some great news to emerge soon from the successful endeavors of Petrobangla companies.

Success in drilling deeper prospects at Titas, Bakhrabad and Srikail could change the scenario.

Some wells drilled recently by SGFL may also add signifi cant new resources.

There is a prospect of fi nding oil as well.

After visiting some drill sites and interacting with technical personnel, I feel optimistic about the discovery of signifi cant new resources soon.

I would like to advise carrying out extensive 2D followed by 3D seismic surveys in the prolifi c Surma Basin, Block 9 and Block 7 areas.

I would also suggest launching a PSC bidding round for land blocks outside BAPEX’s ring-fenced areas.

If 10 exploration rigs are put into operation by 2028, I believe it is possible to add at least 5 Tcf of new gas to recoverable reserves by 2031.

LNG Import Initiative Bangladesh now utilizes 900-1,000 MMCFD of imported LNG through two FSRUs anchored in shallow water off Moheshkhali, Cox’s Bazar.

LNG imports have been stressed by the war in the Middle East and disruption to supply chains.

The interim government of Dr.

M.

Yunus, out of what I believe was a misplaced decision, canceled a signed contract with Summit Group for a new FSRU.

If not, an additional 500 MMCFD of RLNG could have been added by the end of 2026.

The Yunus government also brought several discussions on LNG imports that were at an advanced stage to an end.

During the one and a half years of that government’s tenure, no initiative was taken to increase LNG imports.

The new government is in the process of fi nalizing a contract with a Chinese company.

We hope the government will clarify some controversies arising in the local media about the competence of the Chinese company.

We would suggest resolving the dispute with Summit over the third FSRU in the greater national interest.

At this stage, that would be the best course of action if viewed with positive intent.

Proposals for setting up FSRUs at Khulna and Barishal appear overambitious.

Plans for importing LNG in ISO tanks also appear unrealistic.

Apart from launching initiatives to expand LNG import capacity through FSRUs and land-based terminals, the government has to construct the required additional gas transmission infrastructure.

The two existing gas pipelines from Moheshkhali to Anowara have a combined capacity to evacuate 1,600 MMCFD.

But this would lower the pressure at the inlet of the gas grid to 500 PSI.

Hence, at least one new parallel pipeline must be built by GTCL from Feni to Bakhrabad.

If acquisition of the right of way at a safe distance from the existing pipeline is launched now, along with simultaneous procurement of materials and engagement of contractors, the pipeline may be ready for operation within three years.

It is a national failure that the gas resource discovered at Bhola remains stranded even as the nation suffers from a gas famine.

We have heard with shock and awe that the Prime Minister thinks it could take up to seven years to evacuate gas from the Bhola gas fi elds to the national grid.

As a pipeline professional with about 50 years of proven experience, I can assure you that it should not take more than three years to connect Bhola’s gas resources to the national grid by constructing a 120-km Bhola-Barishal- Khulna pipeline.

Any other proposal to transport the gas by converting it to CNG or LNG would be a waste of time.

We do not think the government needs any additional gas-based power plants at this stage.

Any new fertilizer plant would take 8-10 years.

However, gas supply to Barishal and Khulna could stimulate green industrialization in the region.

For this to happen, the government must professionally assess the proven gas reserve by engaging an internationally accredited reservoir assessor.

GTCL must engage a reputed subsea pipeline developer to design the crossings of three large rivers, along with at least three HDD contractors for the other rivers.

A couple of contractors could be tasked with constructing the land sections of the pipeline.

The existence of a gas transmission facility in the region would encourage IOCs to consider investment in Block 7 and adjoining areas.

Offshore PSC Bidding We have observed a less-thanoptimistic response so far to Petrobangla’s invitation for offshore exploration.

We are not sure that roadshows in Singapore, London and New York would be benefi cial.

We would rather suggest holding a conference in Dhaka and inviting potential bidders.

The deteriorating law-and-order situation in Bangladesh does not provide suffi cient security confi dence to potential investors.

Some regional countries, including Thailand, Vietnam, Malaysia and Indonesia, have also announced bidding rounds.

Those countries have far better records of dealing with IOCs.

Still, we hope that Bangladesh will secure some investment.

Finally, I would suggest strengthening the technical and managerial capacity of Petrobangla and its companies.

Many senior offi cials have reached retirement age.

A huge void of competent offi cials may be created soon.

The government must plan to retain some of them, as their institutional memory will be invaluable.

The government must also move away from exclusive reliance on bureaucrats for gas-system planning and management.

The task of recovering from the crisis is intense but manageable if approached pragmatically.

The bottom line remains an aggressive initiative to explore and develop Bangladesh’s own gas resources, both onshore and offshore.

Domestic gas must contribute at least 50% of the country’s gas requirements through 2040.

LNG import initiatives must also be planned carefully, considering the fi nancial stress they create.

Bangladesh Forms High-Level Committee on Climate Finance and Carbon Trading

The Bangladesh government has formed a 25-member National Committee on Climate Finance (NCCF) to bring climate fi nance, carbon credits and carbon trading activities under a coordinated national framework.

Under a notifi cation issued by the Ministry of Environment, Forest and Climate Change on September 1, Prime Minister Tarique Rahman will chair the committee, while Environment Minister Abdul Awal Mintoo will serve as vice-chair.

Prime Minister’s Special Assistant for Environment, Forest and Climate Change Dr Md Saimum Parvez has been appointed coordinator, while the ministry secretary will serve as member-secretary.

The committee includes State Minister for Environment, Forest and Climate Change Sheikh Faridul Islam, the Prime Minister’s Special Assistant for Health Dr SM Ziauddin Haider, and Adviser Mahdi Amin, who oversees education, primary and mass education, expatriates’ welfare and overseas employment, and labour and employment.

Environment Minister Calls for Immediate Action to Safeguard Bangladesh’s Climate Future

Environment, Forest and Climate Change Minister Abdul Awal Mintoo has stressed that actions taken today to address the climate crisis will determine the safety and security of future generations.

He made the remarks on September 2 while addressing the closing and award-giving ceremony of World Environment Day and Environment Fair 2026 at the Department of Environment auditorium in Agargaon, Dhaka.

Mintoo said effective action must be taken immediately to address the growing risks posed by climate change.

Sustainable development can be achieved by building an environmentally friendly economy that balances environmental protection, social development and economic growth.

He said a green economy based on low-carbon emissions, effi cient use of resources, cleaner production and green employment would play a vital role in meeting the challenges of sustainable development in the 21st century.

India Installs 6.6 GW of Rooftop Solar in First Half of 2026

India added 6.6 GW of rooftop solar capacity in the fi rst half of calendar year 2026, up 136% from 2.8 GW during the same period in 2025, according to Mercom India’s Q2 and H1 2026 India Rooftop Solar Market Report.

Installations reached 3.8 GW in the second quarter, rising 41% from 2.7 GW in Q1 and 136% year-on-year from 1.6 GW in Q2 2025.

Rooftop solar accounted for 33% of India’s total solar installations during the quarter.

Growth was largely driven by the government’s Pradhan Mantri Surya Ghar Muft Bijli Yojana (PM Surya Ghar) program.

By June 2026, rooftop solar systems had been installed in nearly 4.5 million households, reaching about 45% of the program’s target of 10 million households.

Residential projects dominated Q2 installations, accounting for 84% of new capacity.

Industrial projects contributed 10%, commercial installations 5% and government projects 1%.

The capex model represented the majority of quarterly additions

Bangladesh Urges Coordinated Action to Turn Tree Planting into Sustainable Social Movement

Environment, Forest and Climate Change State Minister Sheikh Faridul Islam has called for coordinated efforts to turn tree planting into a sustainable social movement.

He made the remarks while chairing the third meeting of the support taskforce of the National Tree Plantation Cell formed to implement the government’s ‘250 million trees in fi ve years’ programme at the ministry’s meeting room at the Bangladesh Secretariat on September 7.

The state minister said tree planting is crucial to tackling climate change, conserving biodiversity and maintaining ecological balance.

He stressed that the focus should not only be on the number of saplings planted but also on their protection, maintenance and survival.

The meeting was informed that 51.49 million saplings are planned to be planted and maintained in 2026, including around 38.2 million produced by the relevant agencies and 13.3 million procured using their own funds.

NGOs have separately planted around 2.5 million saplings, according to the NGO Affairs Bureau.

US Diesel Price Hits Record $5.90 a Gallon: AAA

The average price of diesel in the United States reached a record $5.90 per gallon on September 7, according to the American Automobile Association (AAA), as supply disruptions linked to the confl ict with Iran pushed fuel prices higher.

The price was about 30 cents higher than a week earlier and signifi cantly above the $3.71 average recorded a year ago.

Rising diesel costs are putting pressure on trucking, agriculture and construction, with businesses potentially passing higher transport costs on to consumers.

The national average for regular gasoline also climbed to around $4.15 a gallon on September 7, up from about $3.20 a year earlier.

Meanwhile, US diesel prices continued to rise, surpassing $6 a gallon nationally by September 10, according to GasBuddy

Chattogram Waste-toEnergy PPP Project Gets Nod

The Cabinet Committee on Economic Affairs (CCEA) on September 9 gave in-principle approval to a proposal for implementing a Waste-toEnergy power generation project in the Chattogram City Corporation area on a Public-Private Partnership (PPP) basis.

The approvals were given at the CCEA meeting held at the Cabinet Division in the city with Finance Minister Amir Khosru Mahmud Chowdhury in the chair.

The proposal was submitted by the Local Government Division.

Chattogram, the country’s second-largest city and a major commercial and industrial hub, generates a substantial volume of municipal solid waste every day

Shipping LNG In ISO-tank And Transport By ‘Virtual Gas Pipeline’

1.EXECUTIVE SUMMARY Bangladesh faces challenges in expanding its LNG supply due to limitations in FSRUs, offshore infrastructure, pipelines, and the country’s shallow-water conditions.

One possible solution is LNG transported in cryogenic ISO tank containers and distributed by a ‘virtual gas pipeline’.

LNG can be loaded into 20- or 40-foot ISO tanks at the exporting country, shipped by conventional container vessels, and then distributed inside Bangladesh by truck, rail, or river barge.

This system is often called a ‘virtual gas pipeline’ because it can deliver natural gas to customers without constructing a continuous gas pipeline.

Recent reporting indicates that Bangladesh is exploring importing LNG from Malaysia in 20- and 40foot ISO tanks for industries, power, and fertilizer plants.

The concept deserves serious consideration as a complement to Bangladesh’s existing and planned FSRU and land-based LNG infrastructure.

The ISO-tank LNG ‘virtual gas pipeline’ is not a substitute for Bangladesh’s large-scale FSRU and land-based LNG terminals.

But at approximately 0.5-2 MTPA, it could become a valuable part of Bangladesh’s energy strategy.

The strongest concept is therefore a Distributed LNG Network combining ISO LNG tanks + conventional container vessels + ports + river barges + rail + trucks + regional LNG hubs + small regasifi cation plants.

Such a system could bring LNG to industrial and power customers even when an FSRU fails.

The most attractive feature may not be the lowest LNG price but a combination of speed, fl exibility, geographic reach, lower infrastructure requirements, and supply security.

The immediate next step should be a detailed Bangladesh feasibility study covering: 1.

Actual ISO-tank capacity and specifi cations 2.

LNG supply source and purchase price 3.

Port suitability at Chattogram, Matarbari, Mongla and Payra 4.

Number and type of container vessels required 5.

Rail, river-barge and truck logistics 6.

Regional LNG hub locations 7.

Small-scale regasifi cation technology 8.

Safety and regulatory requirements 9.

Delivered LNG cost in $/MMBtu 10.

A phased 0.5 MTPA ? 1 MTPA ? 2 MTPA development plan Banglade sh should not try to replace or add FSRUs with ISO tanks.

It should use ISO LNG to create a second, fl exible ‘virtual gas pipeline’ that complements the national LNG and gas-grid system.

2.

How the System Would Work The basic supply chain would be: LNG supplier ? ISO LNG tanks ? conventional container vessel ? Bangladesh port ? truck/rail/barge ? regional LNG hub ? regasifi cation ? customer The process would be: LNG is loaded into certifi ed cryogenic ISO tanks at the exporting country.

The ISO tanks are loaded onto a conventional container or cargo vessel.

The vessel carries the tanks to a suitable Bangladeshi port such as Chattogram, Matarbari, Mongla, or Payra.

The containers are transferred to trucks, railway wagons, or river barges.

They are transported to regional LNG distribution hubs.

At the hub, LNG is transferred to storage and regasifi cation facilities.

The resulting natural gas is supplied through short local pipelines to nearby industries, power plants, fertilizer plants, or other users.ISO LNG containers can be transferred between ships, trucks, and rail, making the system particularly suitable for multimodal transportation.

3.

An Important Limitation ISO-tank LNG is not a replacement for Bangladesh’s large-scale LNG supply system.

A national system requiring approximately 1,000-3,000 MMscfd cannot realistically be supplied entirely through ISO tanks.

The number of containers, ships, cranes, trucks, storage facilities, and handling operations would become enormous.

Therefore, 1 MTPA is technically manageable, while attempting to transport 5-10 MTPA in ISO tanks would create a very large logistical operation.

Approximate requirements are: LNG supply LNG per year Approx.

ISO tanks/year 0.1 MTPA 100,000 tonnes 4,000- 7,000 0.5 MTPA 500,000 tonnes 20,000- 30,000 1.0 MTPA 1 million tonnes 40,000- 60,000 5.0 MTPA 5 million tonnes 200,000- 300,000 These fi gures are approximate and depend on the actual tank capacity and LNG density.

4.

The Best Approach: A Hybrid LNG System The question should not be: ‘FSRU or ISO tanks?’ Instead, Bangladesh should consider a hybrid LNG strategy.

Layer 1 – Bulk LNG Use FSRUs and land-based LNG terminals for national gas-grid supply.

– Large power plants – Major fertilizer plants – Large industrial consumers – Dhaka and other major demand centres Layer 2 – Small-Scale LNG Use ISO-tank LNG for: – Industrial clusters without adequate pipeline supply.

– Fertilizer plants and Captive power plants – Textile factories, Ceramic and glass industries Layer 3 – Inland ‘Virtual Pipeline Use ISO tanks together with river barges, rail, and trucks to reach: Khulna – Barishal – Rajshahi – Northern Bangladesh- Southwestern Bangladesh and Remote industrial areas Three-layer approach allows ISO LNG to complement, not compete with large LNG terminals.

5.

River Barges Could Be Particularly Important Bangladesh has an extensive inlandwaterway network.

Therefore, the system should not depend entirely on road transportation.

Instead of: Port ? Truck ? Factory A more effi cient system could be: Receiving port ? ISO LNG tanks ? River barge ? Inland LNG depot ? Truck/Rail ? Customer Another possible route is: Payra ? River barge/Rail ? Barishal/Khulna region Using barges could substantially reduce road congestion and transportation costs.

Another important advantage, the LNG does not have to be transferred from an LNG carrier to an offshore FSRU.

The LNG remains inside certifi ed ISO tanks throughout the transportation process.

However, this does not eliminate port limitations.

The receiving port must still have suffi cient draft and infrastructure to handle the container vessel.

The advantage is that Bangladesh would no longer require the specialized LNGcarrier/FSRU interface.

6.

The Concept of a Distributed LNG Network The most promising application for Bangladesh is therefore a Distributed LNG Network.

Instead of bringing all LNG to a large terminal, LNG could be distributed among several regional hubs.

For example, a 1 MTPA system could initially be divided approximately as follows: 7.

A Bangladesh-Specifi c 1 MTPA System A practical starting point would be a 1.0 MTPA ISO-LNG system, with the possibility of expanding it to 2 MTPA The proposed fl ow would be: Malaysia/ other LNG supplier ? 40-ft LNG ISO tanks ? Container vessel? Chattogram /Matarbari ? LNG container depot ? Rail/Barge/Truck ? Regional LNG hubs ? regasifi cation ?Customers In short, it would function like a gas pipeline without requiring a continuous physical pipeline.

8.

How Many ISO Tanks Would Be Required? For planning purposes, the document assumes approximately 20 tonnes of LNG per 40-foot ISO tank.

Therefore: 1,000,000 tonnes/year ÷ 20 tonnes/tank = 50,000 loaded tanks/year This means approximately: 50,000 tanks per year- 4,170 tanks per month137 tanks per day This is a substantial logistics operation, but it is not technically impossible.

The actual number should be refi ned after selecting the specifi c ISO tank design, loading capacity, safety requirements, and operating procedures.

9.

Natural Gas Equivalent Approximately 1 MTPA of LNG is equivalent to about 130-135 MMscfd of natural gas.

LNG Approx.

naturalgas equivalent 0.25 MTPA 33 MMscfd 0.50 MTPA 67 MMscfd 1.00 MTPA 134 MMscfd 2.00 MTPA 268 MMscfd 5.00 MTPA 670 MMscfd The proposal therefore suggests initially using ISO LNG for approximately 100- 300 MMscfd of strategically distributed demand, rather than replacing the country’s entire FSRU capacity.

10.

Proposed Five Regional LNG Hubs Hub 1 – Chattogram/Matarbari: 400,000 tonnes/year Potential customers: – Chattogram /Mirsarai industrial areas – Fertilizer and Steel plants – Ceramic industries – Textile factories – Power plants Hub 2 – Dhaka/Narayanganj: 250,000 tonnes/year Possible transportation: Chattogram ? Rail/River Barge ? Narayanganj This could provide gas for industries without new pipelines for every industrial cluster.

Hub 3 – Khulna/Mongla: 150,000 tonnes/year Possible transportation: Chattogram/Mongla ? River Barge ? Khulna Hub 4 – Barishal/Payra: 100,000 tonnes/year Possible transportation: Payra ? River Barge/Rail ? Barishal and surrounding areas Hub 5 – Northern Bangladesh: 100,000 tonnes/year Possible route: Chattogram ? Rail ? Dhaka ? Bogura/Rajshahi/Rangpur.

This could provide LNG to regions where extending the high-pressure gas is diffi cult.

11.

Transportation Strategy Bangladesh should avoid relying entirely on trucks.

A possible initial transportation mix: Transport mode Share LNG/year Rail 40% 400,000 tonnes River barge 35% 350,000 tonnes Truck 25% 250,000 tonnes Total 100% 1,000,000 tonnes This approach would reduce dependence on highways and make greater use of Bangladesh’s rail and inland-waterway infrastructure.

The exact percentages by a detailed feasibility study.

12.

Container Vessel Requirement For conceptual planning, assume that one container vessel can carry approximately 1,000 LNG ISO tanks, with each tank containing approximately 20 tonnes of LNG.

Therefore:1,000 tanks × 20 tonnes = 20,000 tonnes per vessel For 1 MTPA:1,000,000 ÷ 20,000 = 50 vessel loads per year This means approximately 4-5 vessel loads per month.

If larger vessels capable of carrying 1,500-2,000 ISO tanks are available and suitable for the selected port, the number of voyages could be reduced.

13.

Indicative Capital Cost The preliminary capital requirement for a 1 MTPA system could be approximately: Component Indicative CAPEX LNG ISO tanks $250-400 million Main receiving/ depot infrastructure $10-20 million Four to fi ve regional hubs $25-30 million Regasifi cation equipment $100-180 million Truck/rail/barge facilities $50-100 million Safety and control systems $10- 20 million Total $445 million-$750 million These fi gures are conceptual estimates only and should not be treated as EPC quotations.

The ISO-tank fl eet is a major investment, but the tanks can be reused for many years and could potentially be leased rather than purchased.

14.

Economics: The Key Question The most important question is the delivered cost of LNG.ISO-tank LNG will normally have higher transportation and handling costs than bulk LNG delivered through an FSRU.

The ISO-tank system can reduce the need for major infrastructure: – FSRU facilities – Offshore mooring systems – Subsea unloading pipelines – Large LNG storage tanks – Large regasifi cation terminals – Extensive transmission pipelines One published analysis cited in the source material estimated landed ISOLNG costs of approximately $7-9/MMBtu in a particular market.

Bangladesh’s actual cost could be very different because it would depend on the LNG purchase price, shipping distance, port charges, container utilization, transportation costs, and regasifi cation costs.

Therefore, ISO LNG should not necessarily be judged only by its $/ MMBtu cost.

Its other advantages are: – Lower initial infrastructure requirement – Faster implementation – Greater fl exibility – Ability to serve geographically separated customers – Reduced dependence on large pipelines – Better emergency and backup capability – Greater supply resilience 15.

Why This Could Be Valuable for Bangladesh The main attraction of the virtual LNG pipeline is fl exibility.

A conventional gas pipeline requires a large investment before gas can reach the area.

ISO LNG can be delivered wherever there is a suitable road, rail, or waterway connection and an appropriate regasifi cation facility.

This could be particularly useful for industrial areas that are: – Outside the existing gas network – Too far from major transmission pipelines – Experiencing gas shortages – Growing faster than pipeline infrastructure 16.

Recommended Strategy for Bangladesh Bangladesh should not view ISOtank LNG as a replacement for FSRUs.

Instead, the country should develop a complementary three-part LNG system: 1.

Bulk LNG FSRU and land-based LNG terminals for: National gas grid, Major power plants, Major fertilizer plants, and Large industrial consumers 2.

Small-Scale LNG ISO tanks + conventional container vessels for: – Industrial clusters – Fertilizer plants and Captive power – Textile, ceramic and glass industries – Gas-short areas and Emergency supply 3.

Virtual Gas Pipeline ISO tanks + river barges + rail + trucks + regional regasifi cation hubs for: Khulna, Barishal, Northern Bangladesh, Rajshahi and Remote industrial zones This approach allows its LNG supply system to be built in stages instead of depending entirely on a few large facilities.

The source document likewise recommends treating the ISO-tank network as a complementary system to FSRUs and land-based LNG infrastructure

Environment Minister Calls for Immediate Action to Safeguard Bangladesh’s Climate Future

Environment, Forest and Climate Change Minister Abdul Awal Mintoo has stressed that actions taken today to address the climate crisis will determine the safety and security of future generations.

He made the remarks on September 2 while addressing the closing and award-giving ceremony of World Environment Day and Environment Fair 2026 at the Department of Environment auditorium in Agargaon, Dhaka.

Mintoo said effective action must be taken immediately to address the growing risks posed by climate change.

Sustainable development can be achieved by building an environmentally friendly economy that balances environmental protection, social development and economic growth.

He said a green economy based on low-carbon emissions, effi cient use of resources, cleaner production and green employment would play a vital role in meeting the challenges of sustainable development in the 21st century.